Let the original earnings of A and B be Rs.4x and Rs.7x.
New earnings of A = 150% of Rs.4x = Rs.[$150\over100$$\times$4$x$] = Rs.$6x$
New earnings of A = 75% of Rs.7x = Rs.[$75\over100$$\times$7$x$] = Rs.$21x\over4$
So, 6x : $21x\over4$ = 8:7
$6x\times4\over21x$ = $8\over 7$
This does not give x. So, the given data is inadequate.
Let the incomes of A and B be Rs.5x and Rs.4x respectively and let their
expenditures be Rs. 3y and Rs.2y respectively.
The, 5x - 3y = 1600 … (i) and 4x - 2y = 1600 .. (ii)
On multiplying (i) by 2, (ii) by 3 and subtracting, we get 2x = 1600
x = 800
So, A’s income = Rs.5x = Rs.(5 × 800) = Rs.4000