Carlon plans to evaporate a number of gallons of water from 90 gallons of a 15% salt solution to make a 25% salt solution. Which equation can he use to find x, the number of gallons that should be evaporated?

Let the amount of salt in the solution be x, then x/90 = 0.15

x = 90 x 0.15 = 13.5

Let the gallons of water needed to make a 25% salt solution be y, then

13.5/y = 0.25

y = 13.5/0.25 = 54 gallons

Therefore, the amount to be evaporated is 90 - 54 = 36 gallons.