Hello,

you've got a system of 3 simultaneously equations:

I don't know which method you use to solve this system of equations. I solved the EQU1 for y and plugged this term into EQU2. I got:

3x + 5z = 41

-15x + z = -71

Multiply the 1rst equation by 5 and add:

26z = 134. Solve for z. Re-substitute this value and solve for x. Re-substitute the value of z in the EQU2 and solve for y.

You'll get:

The sum of these three numbers is 12

EB