Aloha :)
$$\left.XA-B^T=4X-6E\quad\right|-4X$$$$\left.XA-4X-B^T=-6E\quad\right|+B^T$$$$\left.XA-4X=B^T-6E\quad\right|4X=4\cdot E\cdot X=4\cdot X\cdot E=X\cdot(4E)$$$$\left.XA-X\cdot4E=B^T-6E\quad\right|\text{Distributivgesetz links}$$$$\left.X\cdot(A-4E)=B^T-6E\quad\right|\cdot(A-4E)^{-1}\text{ von rechts multiplizieren}$$$$\left.X=\left(B^T-6E\right)\cdot(A-4E)^{-1}\quad\right.$$