50% is like saying half. They want you to find half of 180, if you know 9 times 2 equals 18, then you already know the answer, all you have to do is add a 0 on the end of the 9.
Or if you're not as strong with mental math, plug into a calculator 180 times the decimal version of 50% which is .5. 180 times .5 equals 90.
