solve by elimination

Question

5x+3y+5z=-16
2x+5y-z=-26
x-4y+2z=10

Answer 1

1st - 5(3rd) ---> 23y - 5z = -66
2nd - 2(3rd) ---> 13y - 5z = -36

subtract those ----> 10y = 30
y = 3

back in 13y-5z=-36
39 - 5y = -36
-5z = 75
z = -15

put y=3 and z=-15 into the original 3rd and you are done.