Answer:
import java.util.Scanner; 
public class Main
{
 public static void main(String[] args) {
     
     //Initialize the prices as constants
     final double PRODUCT_1_PRICE = 2.98;
     final double PRODUCT_2_PRICE = 4.50;
     final double PRODUCT_3_PRICE = 9.98;
     final double PRODUCT_4_PRICE = 4.49;
     final double PRODUCT_5_PRICE = 6.87;
     
     //Declare the other variables
     int productNumber, quantitySold;
     double total = 0.0;
     
     //Create a Scanner object to get input
     Scanner input = new Scanner(System.in);
     
     //Create a while loop
     while(true){
         //Ask the user to enter the productNumber
      System.out.print("Enter the product number or 999 to quit: ");
      productNumber = input.nextInt();
      
      // Stop the loop, if productNumber is 999(sentinel value, you may choose any value you want)
      if(productNumber == 999)
          break;
      
      //Ask the user to enter the quantitySold 
      System.out.print("Enter the quantity sold: ");
      quantitySold = input.nextInt();
      
      //Create a switch statement that works depending on the productNumber entered.
      //For example, if the productNumber is 1, it multiplies the quantitySold by PRODUCT_1_PRICE
      //   and adds the result to the total. If productNumber is 2, it does the same for product 2 ...
      switch(productNumber){
          case 1:
              total += quantitySold * PRODUCT_1_PRICE;
              break;
          case 2:
              total += quantitySold * PRODUCT_2_PRICE;
              break;
          case 3:
              total += quantitySold * PRODUCT_3_PRICE;
              break;
          case 4:
              total += quantitySold * PRODUCT_4_PRICE;
              break;
          case 5:
              total += quantitySold * PRODUCT_5_PRICE;
              break;
      }
     }
  
  //Print the total (when the loop is done)
  System.out.println("The total is $" + total);
 }
}
Explanation:
*The code is in Java.
You may see the explanation as comments in the code.