The more word problems you do and the better you get at reading them carefully, the better you will become at dealing with them. Here's another word problem for you to solve:
Jill has to write a 15 page report. She writes 3 pages on Monday, 4 pages on Tuesday, and 3 pages on Wednesday. How many more pages must she write?
15 - 3 - 4 - 3 = 5 15 - ( 3 + 4 + 3 ) = 5