The ratio between the present ages of A and B is 6:3 respectively. The ratio between A's age 4 years ago and B's age 4 years hence is 1:1. What is the ratio between A's age 4 years hence and B's age 4 years ago? Choose the correct choice from the following options
A) 5 : 4 B) 3 : 0 C) 5 : 1 D) 3 : 2 E) 3 : 7

Rationale: "let the present ages of a and b be 6 x and 3 x years respectively . then , ( 6 x - 4 ) / ( 3 x + 4 ) = 1 / 1 3 x = 8 = > x = 2.67 required ratio = ( 5 x + 4 ) : ( 3 x - 4 ) = 20 : 4 = 5 : 1 . answer : c"
Answer: C