To find how many pizzas only have cheese on them, you'll need to divide the number of pizzas ordered by 3. You'll need to divide the number of pizzas by 3 because 1/3 of the pizzas have cheese on them so by dividing 48 by 3, you'll be finding 1/3 of the pizzas w/ cheese.
48/3=16
Once you've divided 48 by 3, you'll get 16 pizzas w/ cheese.