X+y+z=9 x-y-z=-1
x-y+z= 21
Which value is not in the solution, (x, y,z), of the
system?
1) -8.
2) ---6
3) 11
4) 4

How do you figure out which order to do two step equations in? like which thing do you subtract/add/multiply/divide first? i understand that you do the opposite of whatever's shown on the opposite side, but when?