A and B have their monthly incomes in the ratio 5 : 3, while their monthly expenditures are in the ratio 9 : 4. If they have saved Rs. 18,000 and Rs. 15,000 monthly respectively, then the difference in their monthly incomes is?

Let A's income = 5x, B's income = 3x. Let A's expenditure = 9y, B's expenditure = 4y. Savings: A saves 5x - 9y = 18000, B saves 3x - 4y = 15000. Solving: multiply second eq by 2.25: 6.75x - 9y = 33750. Subtract first eq: 1.75x = 15750, so x = 9000. A's income = 5x = 45000, B's income = 3x = 27000. Difference = 45000 - 27000 = 18000.