The task is to generate the correct answer for a given math problem.

Input: Consider Input: Problem: by selling an article for $ 195 , a person gains $ 45 . what is the gain % ?

Output: 30 %

Input: Consider Input: Problem: a solid yellow stripe is to be painted in the middle of a certain highway . if 1 gallon of paint covers an area of w square feet of highway , how many gallons of paint will be needed to paint a stripe of t inches wide on a stretch of highway m miles long ? ( 1 mile = 5,280 feet and 1 foot = 12 inches )

Output: ( 5,280 mt ) / 12 w', 'b ) ( 5,280 pt ) / 12 m', 'c ) ( 5,280 pmt ) / 12', 'd ) ( 5,280 ) ( 12 m ) / pt', 'e ) ( 5,280 ) ( 12 p ) / mt'

Input: Consider Input: Problem: at the end of the month , a certain ocean desalination plant ' s reservoir contained 30 million gallons of water . this amount is twice the normal level . if this amount represents 75 % of the reservoir ' s total capacity , how many million gallons short of total capacity is the normal level ?
Output: 20