Step 1 - We choose to expand across the first row, as directed.
Step 2 - We now form the minors for each entry in the first row.
The minor of the 1,1 entry is the determinant of the submatrix formed by removing the first row and column: $$\begin{vmatrix} 1 & 0 \\0 & 3\end{vmatrix}.$$
The minor of the 1,2 entry is the determinant of the submatrix formed by removing the first row and the second column: $$\begin{vmatrix} 2 & 0 \\1 & 3\end{vmatrix}.$$
The minor of the 1,3 entry is the determinant of the submatrix formed by removing the first row and the third column: $$\begin{vmatrix} 2 & 1 \\1 & 0\end{vmatrix}.$$
Step 3 - We can write the minor and cofactor expansion along the first row: