Linear Algebra- Matrix Inverse

[Roni1985]

EDIT: someone helped me.
Thanks.

Homework Statement

http://rotter.name/User_files/nor/4d13a8a45ba10325.jpg
I can't solve the second part of the question.

Homework Equations

The Attempt at a Solution

I tried augmenting B and I and doing rref on the augmented matrix
and I tried using determinants

Z = a(ek − fh) + b(fg − kd) + c(dh − eg)

but these two methods are very long. Is there any other method here ?
I think doing rref is shorter but it's still a lot of work.

 

[mrmiller1]

Guass-Jordan elimination