There may be change to the determinant for each row op used, depending on the row operation:
You should know that:
1. Multiplication of a row by a constant multiplies the determinant by that constant.
2. Switching two rows changes the sign of the determinant.
3. Replacing one row by that row + a times another row has no effect on the determinant.
So you need to look at the row ops you did and make the appropriate changes to the determinant.
the determinant of A is indeed 14. Here's a useful site, to help you check your answers:
Matrix calculator