Write down the solution for this math problem: Solve -9*f + 13*f = -28 for f.
answer: -7

Write down the solution for this math problem: Solve -21*r = 21*r - 15*r - 81 for r.
answer: 3

Write down the solution for this math problem: Solve -26*j - 735 + 579 = 0 for j.
answer: -6

Write down the solution for this math problem: Solve a = 3*a - 8 for a.
answer:
4