To solve this, you need to subtract 180 from 400: (400-180=220). After that (I used the fraction/proportion/variable way, but there are others), so 220/400=%(p)/100. Multiply diaganolly, so 400*p=400p, which is equal to 220*100=22000. Therefore, 400p=22000. Now, you have to isolate the variable by dividing both sides by 400: 400p/400=p, and 22000/400=55. Therefore, p=55, or %=55, so the answer is 55%, or C.
