How does the fact that A isn't a square n x n matrix change how to do this question? i know that if A is an invertible n x n matrix, the solution would be $\displaystyle x = A^{-1}b $...

Suppose A is a 3 x 4 matrix and there exists a 4 x 3 matrix C such that $\displaystyle AC = I_{3} $ (the 3x3 identity matrix). Let b be an arbitrary vector in $\displaystyle \mathbb{R}^3$. Produce a solution of $\displaystyle Ax=b$