Question: What is the solution?

Solve 7*r - 20*r = -13 for r.

Answer: 1

Question: What is the solution?

Solve 2*y + 283 = 277 for y.

Answer: -3

Question: What is the solution?

Solve 0 = 209*u - 103*u + 586*u - 12456 for u.

Answer: 18

Question: What is the solution?

Solve -282 + 166 = -29*i for i.

Answer:
4