necessary and sucient condition on q for 3 to be a primitive root modulo p

Let p, q be odd primes with p = 2q + 1.

Find a necessary and sucient condition on q for 3 to be a primitive
root modulo p.

I guess you can use the same type of proof as is here, http://mathhelpforum.com/number-theo...tive-root.html.

Salahuddin
Maths online