Problem Solving

I can't understand this problem for the life of me......please help!

Do you know the Answer?

I guess, Nothing great in this prob. We need to find out the necessary terms.

Since this is addition table, we can set up the following equations

1st Row:
4 + x = 1 ==> x = -3

4 + y = -5 ==> y = -9

2nd Row:
e + (-3) = 7. So e = 10

So n = e + y = 10 + (-9) = 1

10 = e + z = 10 + z. z = 10 - 10 = 0

Since we have z = 0, then m = 4 + 0 = 4
Now we have m = 4 and n = 1 and their sum is 5

No need to use 3rd row if you are confident. Otherwise, use third row to confirm the values of x, y and z.

the answer is 5

you are correct, Thank you so much.....i don't know why I couldn't figure it out