Question:
Solve 213 - 173 = 10*r for r..

Answer:
4

Question:
Solve -10*x - 9*x = -8*x for x..

Answer:
0

Question:
Solve 698 - 38 = -660*k for k..

Answer:
-1

Question:
Solve 7261*k - 1345*k = -15695*k - 657179 - 769147 for k..

Answer:
-66