Let the monthly salaries of M, N, S, and P be represented by \( m \), \( n \), \( s \), and \( p \), respectively.
1. From the first statement, the average of the monthly salaries of M, N, and S is ₹4000:
\[
\frac{m + n + s}{3} = 4000 \implies m + n + s = 12000.
\]
2. From the second statement, the average of the monthly salaries of N, S, and P is ₹5000:
\[
\frac{n + s + p}{3} = 5000 \implies n + s + p = 15000.
\]
3. We are given that the monthly salary of P is ₹6000:
\[
p = 6000.
\]
Now, subtract the first equation from the second equation:
\[
(n + s + p) - (m + n + s) = 15000 - 12000 \implies p - m = 3000.
\]
Substitute \( p = 6000 \):
\[
6000 - m = 3000 \implies m = 3000.
\]
The monthly salary of M is ₹3000. To find the percentage of M's salary with respect to P's salary, we use the formula:
\[
\text{Percentage} = \left( \frac{m}{p} \right) \times 100 = \left( \frac{3000}{6000} \right) \times 100 = 50%.
\]
Thus, the correct answer is (A) 50%.