Thanks, I can do it with the methods you suggested. However, the determinant section in my book comes after the section with these problems, so I'm kinda unsure if this method will be accepted. But thanks anyway.
Well, for # 2, you could work with the row-reduced (upper triangular) versions of each matrix, and then focus on the last row-last column entry. You could do the same with # 1, after factoring.