Question:
Solve 0*y = 5*y - 20 for y..

Answer:
4

Question:
Solve 0 = -510*r + 6319 - 11789 - 12380 for r..

Answer:
-35

Question:
Solve -45 = -930*z + 921*z for z..

Answer:
5

Question:
Solve 609*x = 634*x - 477 - 48 for x..

Answer:
21