What is the answer to ax - c = b

Depends on what you are talking about, what is A,x,c and b.
If A is an invertible matrix and x,c,b are vectors of correct dimensions you get
Ax=b+c
x=A^(-1)(b+c)
if x is a variable and A,c,b are constants you get
Ax=b+c
x=(b+c)/A