Minor of any element of the determinant is the submatrix , if we leave element's row and column .
For example
4 5 6
A = 7 8 9
10 11 12
If we want to calculate the minor of 4 element , then we know this element is in first row and in first column , so we leave this first row and first column
8 6 minor of 4 = 11 12 With this way , you can calculate minor of each and every element of determinant .