Which letter will replace the question mark in the image below ?

Question

Answer 1

N is in the 6+4+4(numbers in its square) = 14th position in the alphabet series
similarly L = 4+1+7 = 12th letter
U = 10+6+5 = 21st letter
therefore
14+2+1 = 17 = Q

Answer 2

Q is the answer.
It's very simple. In all three squares the addition of the three corners is equal to the 4th one, the number represents the sequential number in the alphabet set.
In the 4th square the addition of the 3 corners is 17, it means the 17th alphabet viz. Q.