@aha926076
Misal: R: Umur Robi, b: Umur Soni
R = 15 + b .... (i)
R - y = 2 (b - y) .... (ii)
sub. (i) ke (2)
15 + (b - y) = 2 (b - y)
15 = (b-y)
Jawab C. 15