i've been asked to find the greatest value of $\displaystyle \frac {1}{x}$ from $\displaystyle 3(x + 2)^2 + 5$ the answer is 1/5 but i was wondering if someone could show me how they would come to that answer, thanks

ps there is supposed to be a function symbol (f) in front of the x but i don't know how to write it out