$($a$)$ Write a MATLAB function that accepts as INPUT an n$-$by$-$n upper triangular matrix U along with a column n$-$vector, b and gives as OUTPUT a solution x of $Ux=b$ if such a solution exists.

$($b$)$ Write a MATLAB function that accepts as INPUT an n $-$by$-$n lower triangular matrix L along with a column n $-$vector, b and gives as OUTPUT a solution x of $Lx=b$ if such a solution exists.