The annual income of A and B are in the ratio 3 : 4. If the income of A is 3x, the income of B is 4x. Their annual expenditure is in the ratio 5:7, if A's expenditure is 5y, B's expenditure is 7y. Each of them saves 15000 per month.

=> 3x - 5y = 15000 and 4x - 7y = 15000

3x - 5y = 15000

=> y = (3x - 15000)/5

Substituting in 4x - 7y = 15000

=> 4x - 7*(3x - 15000)/5 = 15000

=> 20x - 21x + 105000 = 75000

=> x = 30000

**This gives the income of A as 90000 and of B as 120000**