Define functions and verify to get the desired result.
Let h(x)=x3,g(x)=x2 and f(x)=x
Then, [ho(gof)](x)=h(g(f(x)))
=h(g(x))
=h(x2)
=x6…(1)
Now, [(hog) of](x)=(hog)(f(x))
=(hog)(x)
=h(g(x))
=h(x2)
=x6…(2)
Comparing equation (1) and (2), we get
ho(gof)=(hog) of
Therefore, composition of functions is associative
Hence, the given statement is True.