Question:
Solve 40 = -20*o + 30*o for o..

Answer:
4

Question:
Solve 75*y + 1628 = 199*y + 512 for y..

Answer:
9

Question:
Solve -7*d + 273 - 103 = -17*d for d..

Answer:
-17

Question:
Solve -74816*r + 149648*r - 459 = 74823*r for r..

Answer:
51