question: Teacher asked me this: Solve 0 = -3*x - 4*x - 21 for x.
++++++++++
answer: -3

question: Teacher asked me this: Solve 316*b + 11530 + 13061 = 9*b + 7092 for b.
++++++++++
answer: -57

question: Teacher asked me this: Solve -7800 = -201*n + 50*n - 109*n for n.
++++++++++
answer: 30

question: Teacher asked me this: Solve 243*u - 57*u - 2046 = 0 for u.
++++++++++
answer:
11