f'=-3(-3)/(2-3x)^4

f"=-36/(2-3x)^5

now look at f', and f" at each side of 2/3, say at .5, and at 1.0

I will do the 1.0 side...

f=1/(2-3)^3=1

f'=9/(2-3)^4= positive 9, high slope

f"=-36/(2-3)^5=36 positive, curving up

now the .5 side.

f=1/(2-1.5)^3=8

f'=9/(2-1.5)^4=9*64 positive, going upwards

f"=-36/(.5)^5=-1152 negative curving down,slope is reducing.

Now graph it on your calculator and take a look