Question:
Solve 0 = 20*d - 15*d + 5 for d..

Answer:
-1

Question:
Solve 714*z = 5291 - 293 for z..

Answer:
7

Question:
Solve 0 = 9*v + 16*v - 50 for v..

Answer:
2

Question:
Solve 242 = 199*w - 2942 for w..

Answer:
16