Its 18....................................
Fractional index means "xth root of". Negative index means a fraction. So together, what it really means is:
![\frac{1}{\sqrt[5]{32}} = \frac{1}{2}.](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B%5Csqrt%5B5%5D%7B32%7D%7D%20%3D%20%5Cfrac%7B1%7D%7B2%7D.)
F(x)=x^2+x+5
then
F(3) would be the function evaluated at x=3, or 17.
anytime you see F(3) it is just whatever formula you are looking at evaluated when the variable is equal to 3.