Bài giải:

$\begin{align}  & \frac{\left( 3\frac{3}{4}:\frac{1}{4}+2\frac{2}{5}\times 1\frac{1}{4} \right)-\left( \frac{7}{2}\times \frac{4}{5}-1\frac{1}{5}:\frac{3}{2} \right)}{\left( 1\frac{1}{2}+\frac{3}{4} \right)\times y}=64 \\  & \frac{\left( 15+3 \right)-\left( \frac{14}{5}-\frac{4}{5} \right)}{\frac{9}{4}\times y}=6 \\ \end{align}$

$\begin{align}  & \frac{18-2}{\frac{9}{4}\times y}=6 \\  & \frac{16}{\frac{9}{4}\times y}=6 \\ \end{align}$

16 : $\frac{9}{4}\times y$ = 6

$\frac{9}{4}\times y$ = 16 : 6

$\frac{9}{4}\times y$= $\frac{16}{6}$

$y=\frac{16}{6}:\frac{9}{4}$

$y=\frac{32}{27}$