Concavity & Inflection point(s)

This is the problem: https://webwork.math.lsu.edu/webwork...6cd14f7771.png

I have to find:

A) critical values = 0

B) where f(x) is increasing = (0,inf)

C) where f(x) is decreasing = (-inf,0)

D) local maxima at x = none

E) local minima at x = 0

**F) concave up =**

**G) concave down =**

**H) inflection point(s) at x =**

I) horizontal asymptote(s) y = 3

J) vertical asymptote(s) x = none

I was able to figure out everything excluding F, G, and H -as you may have noticed. I know that I have to find the second derivative of the original function however when I tried this was what I got:

$\displaystyle \frac{-150(x^4-2x^3+50x^2-50x+625)}{(x^2+25)^2}$

Would someone please help me?