We are given a 4x4 matrix with some letters in place of numbers. To solve this, we observe the pattern of numbers and letters in the table.
- In the second row, we have "L" and "S." It seems that "L" and "S" correspond to the numeric positions in the alphabet (L = 12, S = 19).
- For the third row, we have "P" and the missing letter '?'.
By applying a similar pattern, we deduce that the letter corresponding to '?' should be 'M', which fits the pattern. Therefore, the letter that should be placed in '?' is 'M'.