\begin{equation*}
\begin{split}
& 3\frac{3}{4}\times 5\frac{3}{5}\\\\
& \left(\frac{12}{4} + \frac{3}{4}\right) \times \left(\frac{25}{5} + \frac{3}{5}\right)\\\\
& \frac{15}{4} \times \frac{28}{5}\\\\
& \frac{\cancelto {3}{15} \times \cancelto {7}{28}}{\cancelto {1}{4} \times \cancelto {1}{5}}\\\\
& 21
\end{split}
\end{equation*}
