When you solve a problem involving money, what can a negative answer represent

Means you owe money.  

I have 100 dollars in by bank, I spend 150 dollars.  

100 - 150 = -50 that means I owe 50 more dollars. 

You have a deficit. You do not have enough or you owe money. It means you are in the "red." It means that the (negative) answer is what you still need to be balanced or not owe anything.