frank is 15 years younger then john . in 3 years john will be twice as old as frank . how old will frank be in 4 years ?  Pick:  A) 8  B) 10  C) 12  D) 14  E) 16

Rationale: frank is 15 years younger then john - - > f + 15 = j ; in 5 years john will be twice as old as frank ( in 3 year john will be j + 3 years old and frank will be f + 3 years old ) - - > j + 3 = 2 * ( f + 3 ) - - > ( f + 15 ) + 3 = 2 * ( f + 3 ) - - > f = 12 ; in 4 years frank will be 12 + 4 = 16 years old . answer : e .
Answer: E