Hi Marissa.
Here's how you do it:
 Guess at the price of the sleeping bag: I will start by guessing it is $15.
 Calculate how much the mess kits cost based on the guess and the first bill. The first bill is $37 and the sleeping bag is $15, so that leaves $22 for the mess kits. That makes each mess kit $11.
 Check the costs of the two items with the second bill and see if they add up. The second bill is for one mess kit ($11) and 2 sleeping bags ($15+$15), so that adds up to $41  much less than the actual cost of $56.
 Go back to step 1 and adjust your guess for the cost of the sleeping bag  try to watch to see whether you should go up or down in your guess.
You should eventually find the price of both items.
Cheers,
Stephen La Rocque.
