Correct option is C
The present age of A = 12 years
The present age of B = 12 – 4 = 8 years
The present age of C = 13 – 8 = 5 years
The present age of D be d years
ATQ,
(12+5)/(8+d)=17/15
15-8=d
7=d
Required answer = 12-7=5 years