I guess we're just looking for patterns in the operations. If it's a table, it must be that each number 4, e, & f is added to x, y, and z, individually. If you look at the first row, you will see that 4+x= 1and 4+y=-5. This simply means that x and y are equal to -3 and -9, respectively. But we still need m and we assume that the other rows follow the same patterns. So for row e, 7 is the result of e+(-3); therefore e must equal 10, right? On the same row, we notice that 10+z=10, then z =0. There for 4+0=4. The table ends up looking like this:

+ |-3 -9 0
4 | 1 -5 4
10 | 7 1 10
5 | 2 -4 5

m+n=4+1=5

Hopefully this helps

check attachement for solution

It is great explanation. Thank you