Let the monthly incomes of A and B be 13x and 7x respectively.
Let the expenditure of A and B be 9y and 7y respectively.
It is given that the saving of A and B are Rs 8000 each
∴ 13x – 9y = 8000 (1)
7x – 7y = 8000 (2)
Saving these two equations, you will obtain
y = -12000/7 and x = -4000/7
Since x and y are negative values so, the expenditure and incomes of A and B are negative values which is not possible