Rick held a fundraiser and is figuring out who still owes money. He marked on a sheet how much everyone has promised to contribute, but he forgot to note how much some people had actually paid. Altogether, everyone has promised to contribute $400, and Rick has actually received $285. Sally, Amy, Derek, and Carl all still owe money. Sally and Carl both owe equal amounts, Amy owes $30, and Derek owes half as much as Amy. How much, in dollars, do Sally and Carl each owe? Think carefully first, then make a decision:
In total, Rick is still owed 400 - 285 = $115. Derek owes half as much as Amy, so he owes $30 / 2 = $15. This means that Sally and Carl owe a combined total of $115 - $30 $15 = $70. As they owe equal amounts, they therefore owe $70 / 2 = $35 each. So, the answer is 35.