If grapes are 91% water and raisins are 19% water, then how many kilograms did a quantity of raisins, which currently weighs 9 kilograms, weigh when all the raisins were grapes? (Assume that the only difference between their raisin-weight and their grape-weight is water that evaporated during their transformation.) Answers:
A) 63 B) 72 C) 81 D) 90 E) 99

Rationale: "let x be the original weight . the weight of the grape pulp was 0.09 x . since the grape pulp is 81 % of the raisins , 0.09 x = 0.81 ( 9 kg ) . then x = 9 * 9 = 81 kg . the answer is c ."
Answer: C