อ่านโค้ด เข้าใจเหตุผล
แล้วลองด้วยตัวเอง

table 50102 "SBC Practice"
{
    Caption = 'StartBC practice';
    DataClassification = CustomerContent;
    fields
    {
        field(1; "No."; Code[20])
        {
            Caption = 'No.';
            NotBlank = true;
        }
        field(2; Description; Text[100])
        {
            Caption = 'Description';
        }
    }
    keys
    {
        key(PK; "No.")
        {
            Clustered = true;
        }
    }
}

page 50102 "SBC Practice List"
{
    Caption = 'StartBC practice records';
    PageType = List;
    SourceTable = "SBC Practice";
    ApplicationArea = All;
    UsageCategory = Lists;
    layout
    {
        area(Content)
        {
            repeater(Records)
            {
                field("No."; Rec."No.")
                {
                    ApplicationArea = All;
                    ToolTip = 'Specifies the unique code for a training record.';
                }
                field(Description; Rec.Description)
                {
                    ApplicationArea = All;
                    ToolTip = 'Specifies the description of the training record.';
                }
            }
        }
    }
}

permissionset 50102 "SBC PRACTICE"
{
    Assignable = true;
    Caption = 'StartBC practice records';
    Permissions = tabledata "SBC Practice" = RIMD,
                  table "SBC Practice" = X,
                  page "SBC Practice List" = X;
}

codeunit 50100 "SBC Calculation"
{
    procedure CalculateAmount(Quantity: Decimal; UnitPrice: Decimal): Decimal
    begin
        if Quantity < 0 then
            Error(NegativeQuantityErr);
        if UnitPrice < 0 then
            Error(NegativePriceErr);
        exit(Round(Quantity * UnitPrice, 0.01));
    end;

    var
        NegativeQuantityErr: Label 'Quantity must be zero or greater.';
        NegativePriceErr: Label 'Unit price must be zero or greater.';
}

page 50101 "SBC Calculation Exercise"
{
    PageType = Card;
    ApplicationArea = All;
    UsageCategory = Tasks;
    Caption = 'StartBC calculation exercise';

    layout
    {
        area(Content)
        {
            group(Inputs)
            {
                Caption = 'Inputs';
                field(QuantityInput; Quantity)
                {
                    ApplicationArea = All;
                    Caption = 'Quantity';
                    ToolTip = 'Specifies a nonnegative training quantity.';
                }
                field(PriceInput; UnitPrice)
                {
                    ApplicationArea = All;
                    Caption = 'Unit price';
                    ToolTip = 'Specifies a nonnegative training price.';
                }
                field(AmountOutput; Amount)
                {
                    ApplicationArea = All;
                    Caption = 'Amount';
                    Editable = false;
                    ToolTip = 'Shows the calculated training amount.';
                }
            }
        }
    }
    actions
    {
        area(Processing)
        {
            action(CalculateTraining)
            {
                Caption = 'Calculate';
                ApplicationArea = All;
                Image = Calculate;
                ToolTip = 'Calculates the amount from the current inputs.';
                trigger OnAction()
                var
                    Calculation: Codeunit "SBC Calculation";
                begin
                    Amount := Calculation.CalculateAmount(Quantity, UnitPrice);
                end;
            }
        }
    }
    trigger OnOpenPage()
    begin
        Quantity := 2;
        UnitPrice := 150;
    end;
    var
        Quantity: Decimal;
        UnitPrice: Decimal;
        Amount: Decimal;
}

tableextension 50100 "SBC Customer" extends Customer
{
    fields
    {
        field(50100; "SBC Training Note"; Text[100])
        {
            Caption = 'Training note';
            DataClassification = CustomerContent;
        }
    }
}

pageextension 50100 "SBC Customer Card" extends "Customer Card"
{
    layout
    {
        addlast(General)
        {
            field(SBCTrainingNote; Rec."SBC Training Note")
            {
                ApplicationArea = All;
                ToolTip = 'Specifies a note used only for the StartBC training exercise.';
            }
        }
    }
    actions
    {
        addlast(Processing)
        {
            action(SBCShowTrainingAmount)
            {
                Caption = 'Calculate training amount';
                ApplicationArea = All;
                Image = Calculate;
                ToolTip = 'Calculates a training amount without posting a document.';
                trigger OnAction()
                var
                    Calculation: Codeunit "SBC Calculation";
                begin
                    Message(TrainingAmountMsg, Calculation.CalculateAmount(2, 150));
                end;
            }
        }
    }
    var
        TrainingAmountMsg: Label 'Training amount: %1';
}