Answer
(a) $g(x/y)=\frac{x}{y}\sin\left(\frac{x}{y}\right)$, (b) $g(xy)=xy\sin(xy)$,
(c) $g(x-y)=(x-y)\sin(x-y)$
Work Step by Step
(a) Substitute $x=x/y$: $$g(x/y)=\frac{x}{y}\sin\left(\frac{x}{y}\right)$$
(b) Substitute $x=xy$:
$$g(xy)=xy\sin(xy)$$
(c) Substitute $x=x-y$:
$$g(x-y)=(x-y)\sin(x-y)$$
