Solve -66*f - 49*f - 49280 = -56640 for f.
Solve this plz.

A: 64

Solve 21 = -128*s + 121*s for s.
Solve this plz.

A: -3

Solve 1078*r = 1065*r + 78 for r.
Solve this plz.

A:
6