The ratio of ages of A and B is 4 : 5. Six years hence, the ratio becomes 6 : 7. The present age of B is:

मान लीजिए आयु 4x और 5x है। (4x+6)/(5x+6) = 6/7 => 28x + 42 = 30x + 36 => 2x = 6 => x = 3। B की आयु = 5 * 3 = 15 वर्ष।