Question:
Solve -58 - 86 = -8*r - 10*r for r..

Answer:
8

Question:
Solve -40 = -13*r + 25 for r..

Answer:
5

Question:
Solve -1856*f - 45327 = -293*f for f..

Answer:
-29

Question:
Solve -84 = -17*o - 254 for o..

Answer:
-10