I think the second equation should be x + 3y = -1.
System determinate:
System determinate is nothing but the co-efficient matrix
Therefore, co-efficient matrix is
x-determinate
x determinate is obtained by replacing the first column of the system determinate by solution column.
Therefore, x-determinate is
y-determinate
y determinate is obtained by replacing the second column of the system determinate by solution column.
Therefore, y-determinate is