for example:
ax+by+cz=j
dx+ey+fz=k
gx+hy+iz=l
the coefficient matrix would be [[a,b,c][d,e,f][g,h,i]] and the matrix for the variable x is [[j,b,c][k,e,f][l,h,i]], the matrix for variable y is [[a,j,c][d,k,f][g,l,i]], the matrix for variable z is [[a,b,j][d,e,k][g,h,l]]
to find the solutions to the variables would be the following:
Det( X matrix)/Det( Co-eff matrix) = X
Det( Y matrix)/Det( Co-eff matrix) = Y
Det( Z matrix)/Det( Co-eff matrix) = Z
the calculator comes built in with det so that saves you a ton of work already. you can create a matrix just using the [ and the ].
but there is a easier way to solve for linear equations, the rref where you just put practically everything into just one matrix and your output is on the last column output.