Working notes for the above answer is as under

we have been given that , At the time of purchase, the stock traded at A$45/share and the exchange rate was A$1.5/US$.

So at the time of purchase what we have in dollar is

=45 /1.5

= A$30/share

Now , the stock trades for A$30 and the exchange rate is A$1.2/US$ when you close your position

So what we have at the time of losing is 30/1.2

=What You receive is $ 25

So previously at the time of purchase your value in us$ 30

Now at the time of trade its vale is Us$ 25

So upon return in $ is

= US$30- US$-25

= US$5

Particular
Amount in $

Purchase  value
30

Sale Value
25

Return
-5

Now we will calculate return

=  -5/30

=  -0.1667