Q: What is the solution?
Solve -13*x + 9*x - 4 = 0 for x.

A: -1

Q: What is the solution?
Solve 0 = 11*r - 3916 + 3663 for r.

A: 23

Q: What is the solution?
Solve 13 - 17 = -u for u.

A:
4