Relative velocity of 2 particles

[DespicableMe]

Homework Statement

Two particles are emitted from opposite ends of a linear particle accelerator, one with a speed of 0.5 c and the other with a speed of 0.6 c, relative to the accelerator.

What is the relative speed of the two particles?

Homework Equations

V_PE = V_PA + V_AE

The Attempt at a Solution

I understand that there is relative velocity between:
A particle to the accelerator (V [subscript] PA )
A particle to the other particle ( V [subscript] PP)

How would I continue?
We haven't gone in depth for Rel. vel. between two moving objects - only between an object and the ground, but that section was very brief.

 

[kuruman]

You need to add the velocities relativistically. See for example
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html