Voltage on a point charge from a stick of charge

[Colts]

Homework Statement

In the figure the rod has a charge density of ßx, where x=0 is the left end of the rod, etc. Find the electric potential energy of the point charge q a distance a from the end of the rod and lying along the rod's axis.
http://www.usi.edu/science/physics/pickett/206/4p4f1.jpg

Homework Equations

V=$\frac{q}{4\pi\epsilon r}$

The Attempt at a Solution

Since it is voltage from the whole rod it should be an integral, but where I'm not sure at is what should be on top of the fraction

The integral is from 0 to L
$\int\frac{q}{4\pi\epsilon (a+L-x)}dx$
or
$\int\frac{\beta x}{4\pi\epsilon (a+L-x)}dx$

 

[haruspex]

To calculate the voltage where the point charge is, the point charge itself is irrelevant. You want the voltage generated by the charge distribution on the rod, so it's the second integral.