Question: What is the solution?

Solve -13*r + 9 = -16*r for r.

Answer: -3

Question: What is the solution?

Solve 20646*z - 2056732 - 400142 = 0 for z.

Answer: 119

Question: What is the solution?

Solve -505 = 850*a - 749*a for a.

Answer: -5

Question: What is the solution?

Solve 12*r = -4 - 92 for r.

Answer:
-8