Question: What is the solution?

Solve 0 = 4*w + 793 - 821 for w.

Answer: 7

Question: What is the solution?

Solve -16*k + 0*k - 40 = -88 for k.

Answer: 3

Question: What is the solution?

Solve 0 = -2*l - 4 + 2 for l.

Answer: -1

Question: What is the solution?

Solve -18*a = 21*a - 40*a + 21 for a.

Answer:
21