The rate $($in liters per minute$)$ at which water drains from a tank is recorded at half$-$minute intervals. Use the average of the left$-$ and right$-$endpoint approximations $($assuming $6$ rectangles$)$ to estimate the total amount of water drained during the first $3$min.

$\backslash$table$[[tmin,0,0\mathrm{.}5,1,1\mathrm{.}5,2,2\mathrm{.}5,3],[\frac{1}{m}in,40,38,36,34,32,30,28]]$