Final answer:
The cost of a medium pizza is found by subtracting the cost of a small pizza ($11.25) and a large pizza ($17.50) from the total cost ($43.80), which results in a medium pizza cost of $15.05.
Step-by-step explanation:
To calculate the cost of a medium pizza, we'll take the total cost of all three pizzas and subtract the known costs of the small and large pizzas. We are given that a small pizza costs $11.25 and a large pizza costs $17.50. The total cost for one small, one medium, and one large pizza is $43.80.
So, the cost of a medium pizza can be found using the equation:
Cost of Medium Pizza = Total Cost - Cost of Small Pizza - Cost of Large Pizza
Cost of Medium Pizza = $43.80 - $11.25 - $17.50
Cost of Medium Pizza = $43.80 - $28.75
Cost of Medium Pizza = $15.05
Therefore, the medium pizza costs $15.05.