Given:

Here x represents the number of pizzas and y represents the number of sandwiches.
Buy 3 pizas:
Substitute x=3 in the given expression, and solve for y.

Thus, you can buy 10 sandwiches if you buy 3 pizza.
Assume you buy 6 pizzas.
Substitute x=6 in the given expression.

Thus, you can buy 4 sandwiches if you buy 6 pizzas.