Question: What is the solution?

Solve -25*r + 40*r = 75 for r.

Answer: 5

Question: What is the solution?

Solve -6247 = -28*x - 6443 for x.

Answer: -7

Question: What is the solution?

Solve 56 = -40*u + 26*u for u.

Answer: -4

Question: What is the solution?

Solve 13 - 11 = c for c.

Answer:
2