In each square the sum of digits is the count of letter.

count for N = 14 = 6+4+4 count for L = 12 = 4+1+7 ........

Hence the missing letter is Q.

If

4+5+4+5=81 5+6+5+6=16 6+7+6+7=64 1+2+1+?=16

What is the missing number?

Find the value of the question mark in the following puzzle?