Question: What is the solution?

Solve 8*u - u = -21 for u.

Answer: -3

Question: What is the solution?

Solve 0 = -4423*x + 5770*x + 127965 for x.

Answer: -95

Question: What is the solution?

Solve -8904*r + 1337 - 5851 = -13418*r for r.

Answer: 1

Question: What is the solution?

Solve 0 = 362*d + 381*d - 1939 + 8626 for d.

Answer:
-9