Q: Solve 0 = 939*z - 889*z + 800 for z.

A: -16

Q: Solve 9*o = -o + o for o.

A: 0

Q: Solve -2*r - 10 = -12 for r.

A: 1

Q: Solve -135*k + 132*k - 21 = 0 for k.

A:
-7