[tex]\begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hspace{5em}\stackrel{\textit{40\% of 315}}{\left( \cfrac{40}{100} \right)315}\implies 126~\hfill \underset{\textit{after discount}}{\stackrel{315~~ - ~~126}{189}}[/tex]