A. Rs. 3500

**B. Rs. 4000 (Correct)**

C. Rs. 4050

D. Rs. 5000

Explanation:

Let P, Q and R represent their respective monthly incomes. Then, we have:

P + Q = (5050 * 2) = 10100 — (i)

Q + R = (6250 * 2) = 12500 — (ii)

P + R = (5200 * 2) = 10400 — (iii)

Adding (i), (ii) and (iii), we get:

2(P + Q + R) = 33000 = P + Q + R = 16500 — (iv)

Subtracting (ii) from (iv), we get, P = 4000.

P’s monthly income = Rs. 4000