$1$: sum $=0$

$2$: for i $=$ n to $1$

$3$: psum $=0$

$4$: for j $=1$ to i

$5$: psum $=$ psum $+$ L$[$i$,$j$]$

$6$: sum $=$ sum $+$psum

$7$: return sum

$(8$ points$)$ Express the function fm$($n$)$ that represents the overall total number of additions performed by Line $5$ during the execution of the algorithm.