Solve 21*c + 7 = 28*c for c.
Solve this plz.

A: 1

Solve -329*o = -244*o - 510 for o.
Solve this plz.

A: 6

Solve -64*a - 2250 = 800 - 1114 + 2480 for a.
Solve this plz.

A:
-69