Find next number in matrix

Question

I've been struggling with this puzzle for the last few days.

We have square

$$\begin{bmatrix} 3 & 6 & 2 & 8 \\ 2 & 1 & 1 & 3 \\ 1 & 3 & 1 & 4 \\ 5 & 5 & 3 & ? \end{bmatrix}$$

Question is what number we should insert instead of question mark ?

Answer 1

Each row or column $[a\:b\:c\:d]$ has the structure of $a+b-c+1=d$, so $? = 8$.