Answer
The speed parameter is $~~\beta = 0.75$
Work Step by Step
It takes light 6.0 years to travel 6.0 light years.
It takes the particle 8.0 years to travel 6.0 light years.
We can find the speed of the particle:
$v = \frac{6.0~ly}{8.0~y} = 0.75~c$
The speed parameter is $~~\beta = 0.75$
