Question:
Solve 21*d + 90*d - 13*d = 40*d + 2204 for d..

Answer:
38

Question:
Solve 27*s + 72 = 3*s for s..

Answer:
-3

Question:
Solve 527*r + 1140 = 337*r for r..

Answer:
-6

Question:
Solve 0 = -7437370*f + 7437382*f - 204 for f..

Answer:
17