Chapter 2 - Matrices - 2.3 The Inverse of a Matrix - 2.3 Exercises - Page 72: 53

$x=4$

That would mean that $AA$ is equal to the identity matrix; thus the equations we get are: $9-2x=1$, $3\cdot-2+(-3)(-2)=0$, $3x-3x=0$, $-2x+9=1$ The middle two are satisfied and the other two are the same, so $9-2x=1\\8=2x\\x=4$