Question:
Solve 19 = 319*f - 338*f for f..

Answer:
-1

Question:
Solve -67*n = 285 - 754 for n..

Answer:
7

Question:
Solve 1513*d + 5940 = 1117*d for d..

Answer:
-15

Question:
Solve 15 = -562*r + 577*r for r..

Answer:
1