P is three times as old as Q. In 7 years, P will be twice as old as Q. How old was P three years ago?
Choices:
A) 15  B) 18  C) 21  D) 24  E) 27
P = 3Q so Q = P/3   P+7 = 2(Q+7) = 2(P/3+7)   P/3 = 7   P = 21   Three years ago, P was 18.   The answer is 18.
<result>B</result>
P is three times as old as Q. In 7 years, P will be twice as old as Q. How old was P three years ago?