Answer
$u=\frac{5}{2}x.$
$y=\sin{u}.$
Work Step by Step
Working from the inside out:
Take $x$; multiply it by $\dfrac{5}{2}\leftarrow$ "inner function."
Take $\frac{5}{2}x$; take the sine of it $\leftarrow$ "outer fucntion."
$u=\frac{5}{2}x.$
$y=\sin{u}.$
