M N P

x P N

--------------------

S Q N

N Q Q P x

--------------------------

N P M A N

Now, if 'P' stands for 6, 'M' for 4 and 'Q' for 5, then what is the difference between S and Q?

The correct option is B 3
Given, P = 6 , M = 4 and Q = 5.
4 N 6
x 6 N
S 5 N
N 5 5 6 x
N 6 4 A N
Where A = 5 + 6 = 11 so A = 1 & carry over 1 + S + 5 = 14, So S = 8
Therefore,
4 N 6
x 6 N
8 5 N
+N 5 5 6 x
N 6 4 1 N
From the first row of multiplication it is clear that N $\times$ 6 = N

So, N can be either 2 or 4 or 6 or 8 or 0.

also, taking into consideration the second multiplication of N $\times$ N + carryover = 5 (in units place) , only N=2 fits

So, N = 2.

Also, N $\times$ 4 = 2 $\times$ 4 = 8

So, S = 8.

So difference between S and Q is 8 - 5 = 3 (option B)