$\text{Average Speed} = \dfrac{\text{Total Distance travelled}}{\text{Total time taken}}$
Total Distance travelled $=2d$
Total time taken $=$ Time taken from $A$ to $B$ + Time taken from $B$ to $A$
$=\dfrac{d}{60}+\dfrac{d}{90}$
Average speed $=\dfrac{2d}{\dfrac{d}{60}+\dfrac{d}{90}}=\dfrac{2d*180}{5d}=72km/hr$
Hence, option (A) is correct