Question:
Solve 19 = 4*o - 77*o - 54 for o..

Answer:
-1

Question:
Solve 180 - 182 = 87*o + 781 for o..

Answer:
-9

Question:
Solve 4*d - 129 = -39*d for d..

Answer:
3

Question:
Solve 9384 = 1827*r + 4871 - 8592 - 6992 for r..

Answer:
11