Let the monthly incomes be (A, B, C).
From the given averages:
A+B=2×3590=7180
B+C=2×4250=8500
A+C=2×6500=13000
Now add the first two:
(A+B)+(B+C)=7180+8500=15680
A+2B+C=15680
Subtract ((A + C)):
(A+2B+C)−(A+C)=15680−13000
2B=2680⇒B=1340
Now find (C):
B + C = 8500
C = 8500 - 1340 = 7160
Final Answer: ₹7,160