I believe the determinant has already been given and it is 10. (The two previous problems are set up in this same way, simply with 2x2 matrices, and one of them said "hint: we know the determinant is 30" which is what the matrix was equal to.)

I am just not sure where to go from here. I wish I could offer some more beginning steps, but I'm totally stumped. I tried to begin to do the whole minor/cofactor thing by crossing out the first row and first column, but then the first element would be x, and I don't know if that's right/how it'd work.

I really will appreciate any help. (Happy)