M's capital is reduced by Rs. 1,000 every month, and by the \(k\)-th month a total of \(1000k\) has been withdrawn, so his effective capital during month \(k\) is \(35000 - 1000k\), for \(k = 1\) to \(13\).
Sum of M's capital over 13 months = \(13 \times 35000 - 1000(1+2+\cdots+13) = 455000 - 1000 \times 91 = 455000 - 91000 = 364000\).
Similarly, N's capital during month \(k\) is \(22000 + 1000k\), so the sum over 13 months = \(13 \times 22000 + 1000 \times 91 = 286000 + 91000 = 377000\).
Ratio of M's capital to N's capital = \(364000 : 377000 = 28 : 29\) (dividing both by 13000).
Total profit = Rs. 85,500, shared in the ratio 28:29, total parts = 57.
M's share = \(85500 \times \dfrac{28}{57} = 1500 \times 28 = 42000\).
So M's share of the profit is Rs. 42,000.