The first step is to find the cofactors of each of the elements in the first column. We then multiply by the elements of the first row and assign plus and minus in the order:

plus, minus, plus, minus

4x4 example

expand 4x4 example

Now, we expand out each of those 3 × 3 cofactors using the method that we saw before:

cofactor

cofactor 2

cofactor 3

cofactor 4

Now, putting it all together, we have:

4x4

4x4 expand

answer = -279