How do you solve 7- ³√9c = 4?

Answer 1

7 - crt(9c) = 4,
-crt(9c) = 4 - 7,
-crt(9c) = -3,
Multiply both sides by -1:
crt(9c) = 3,
Cube both sides and get:
9c = 27,
c = 3.