Answer:
See Explaination 
Explanation:
#include<iostream>
using namespace std;
//function to enter sales
void Enter_sale(int sales[5][4])
{
 //variables
 int product,person,sale_amount;
 
 cout<<"1. Product 1 \n2. Product 2 \n3. Product 3 \n4. Product 4 \n5. Product 5 \n";
 
 //prompt for product
 cout<<"Enter Product: ";
 cin>>product;
 
 cout<<"1. Sales Person 1 \n2. Sales Person 2 \n3. Sales Person 3 \n4. Sales Person 4 \n";
 
 //prompt for sales
 cout<<"Enter Sales Person: ";
 cin>>person;
 
 //prompt for sales amount
 cout<<"Enter Sales Amount: ";
 cin>>sale_amount;
 
 //adding to previous total sales amount
 sales[product-1][person-1]=sales[product-1][person-1]+sale_amount;
}
//function to check sales by a person
void Check_salesperson(int sales[5][4])
{
 int person,total=0;
 cout<<"1. Sales Person 1 \n2. Sales Person 2 \n3. Sales Person 3 \n4. Sales Person 4 \n";
 
 //prompt for person
 cout<<"Enter Sales Person: ";
 cin>>person;
 
 if(person>=1 && person<=4)
 {
 //printing details of sales by a person
 cout<<"Details of Sales \n";
 for(int i=0;i<5;i++)
 {
 cout<<"Product "<<i+1<<": "<<sales[i][person-1]<<"\n";
 total=total+sales[i][person-1];
 }
 //printing total sales by a person
 cout<<"Total: "<<total<<"\n";
 }
 else
 {
 cout<<"Error!\n";
 }
}
//function to check sales by a product
void Check_product(int sales[5][4])
{
 int product,total=0;
 cout<<"1. Product 1 \n2. Product 2 \n3. Product 3 \n4. Product 4 \n5. Product 5 \n";
 
 //prompt for product
 cout<<"Enter Product: ";
 cin>>product;
 if(product>=1 && product<=5)
 {
 //printing details of sales on a product
 cout<<"Details of Sales \n";
 for(int i=0;i<4;i++)
 {
 cout<<"Sales Person "<<i+1<<": "<<sales[product-1][i]<<"\n";
 total=total+sales[product-1][i];
 }
 //printing total sales on a product
 cout<<"Total: "<<total<<"\n";
 }
 else
 {
 cout<<"Error!\n";
 }
}
int main()
{
 int choice;
 int sales[5][4] = {{0,0,0,0},{0,0,0,0},{0,0,0,0},{0,0,0,0},{0,0,0,0}};
 while(true)
 {
 //Menu
 cout<<"1. Enter Sales\n2. Check Sales by a Person\n3. Check Sales on a Product\n4. Exit\n";
 
 //choice
 cin>>choice;
 switch(choice)
 {
 //if enter sales
 case 1:
 Enter_sale(sales);
 break;
 //if check sales by a person
 case 2:
 Check_salesperson(sales);
 break;
 //if check sales on a product
 case 3:
 Check_product(sales);
 break;
 //if exit
 case 4:
 exit(0);
 //if wrong choice
 default:
 cout<<"Error!\n";
 break;
 }
 }
}