Respuesta :

[tex]\bf \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{30\% of 40}}{\left( \cfrac{30}{100} \right)40}\implies 12[/tex]

Crystal0630
The answer is fifteen