Question

Alex has 4 pizzas if he eats 2 how many will he have left

Answer 1

He have 4
He ate 2
Left: what he had - how many he ate = 4-2 = 2

Answer 2

If Alex has 4 pizzas in total and he eats two , then he has 2 pizzas left.
4 pizzas - 2 pizzas = 2 pizzas.