Rakesh's monthly income is Rs. 4000. To find this, we can use the following steps:
The total income of Rakesh and Suresh is 10100.
The total income of Suresh and Ramesh is 12500.
The total income of Rakesh and Ramesh is 10400.
Adding these three equations gives us 2(P + Q + R) = 33000 or P + Q + R = 16500.
Subtracting the equation for Suresh and Ramesh from this equation gives us P = 4000.
Therefore, Rakesh's monthly income is Rs. 4000.