4x+2y-3z=7 2x+4y+z=35 6x+2y-2z=20 solve the system

Answer 1

#1 + 3(#2) ----> 10x + 14y = 112 or 5x + 7y = 56 (#4)
#3 + 2(#2) ---> 10x + 10y = 90 or 5x + 5y = 45 (#5)

#4 - #5 ---> 2y = 11
y = 5.5
in #5 --> x + 5.5 = 9
x = 3.5

in #2
2(3.5) + 4(5.5) + z = 35
z = 6

I will leave it up to you to check those answers.