Got this in class forgot how to do it

Saline iv fluid bags cost $64.20 for 24, 1000 ml bags from one supplier. another supplier sells 500 ml bags for $2 each. the hospital uses about 10,000, 1000 ml bags each month. nurses report that about half of the bags are more than half full when they are discarded. if you are going to use only one supplier, which would you choose and how much would you save with that choice? show calculator try it! if you buy 1000 ml bags, how many do you need to buy each month? type your answer in the space provided and click on the check answer button.

Witch represents the inverse of the function f(x)=1/4x-12

What is the product? a-3/15a × 5/a-3