A tank holds x gallons of a saltwater solution that is 20% salt by volume. One Fourth of the water is evaporated, leaving all of the salt. When 6 Gallons of water and 12 gallons of salt are added, the resulting mixture is 33 1/3 % salt by volume. What is the value of x? Choose the correct choice from the following choices
A) 37.5  B) 75  C) 100  D) 150  E) 90

Rationale: nope , 150 . i can only get it by following pr ' s backsolving explanation . i hate that . original mixture has 20 % salt and 80 % water . total = x out of which salt = 0.2 x and water = 0.8 x now , 1 / 4 water evaporates and all salt remains . so what remains is 0.2 x salt and 0.6 x water . now 12 gallons salt is added and 6 gallons of water is added . so salt now becomes - > ( 0.2 x + 12 ) and water - - > ( 0.6 x + 6 ) amount of salt is 33.33 % of total . so amount of water is 66.66 % . so salt is half of the volume of water . so ( 0.2 x + 12 ) = ( 0.6 x + 6 ) / 2 = > 0.4 x + 24 = 0.6 x + 6 - > 0.2 x = 18 solving , x = 90 answer : e
Answer: E