// Solve equation [3] for the variable z
[3] z = -2x - 2y + 10
// Plug this in for variable z in equation [1]
[1] x - y + 3•(-2x-2y+10) = 9
[1] -5x - 7y = -21
// Plug this in for variable z in equation [2]
[2] x + 2•(-2x-2?+10) = 3
[2] -3x = -17
// Solve equation [2] for the variable ?
[2] 4? = -3x + 17
[2] ? = -3x/4 + 17/4
// Plug this in for variable ? in equation [1]
[1] -5x - 7•(-3x/4+17/4) = -21
[1] x/4 = 35/4
[1] x = 35
// Solve equation [1] for the variable x
[1] x = 35
// By now we know this much :
x = 35
? = -3x/4+17/4
z = -2x-2?+10
// Use the x value to solve for ?
? = -(3/4)(35)+17/4 = -22
// Use the x and ? values to solve for z
ANSWER: z = -2(35)-2(-22)+10 = -16
