$($a$)$ Solve for $x_1,x_2,x_3$ using Cramer's rule.

$($b$)$ Solve for $x_1,x_2,x_3$ using $x=A^{-1}B.$

$($c$)$ In Matlab, solve for $x_1,x_2,x_3$ using Gaussian elimination.

$($d$)$ In Matlab, solve for $x_1,x_2,x_3$ using $x=A^{-1}B.$