Using the ideal gas law we can determine this:
PV = nRT
n and R are constants but V and T are doubled:
that is the same as multiplying the entire equation by 2:
2(PV) = 2(nRT)
Therefore if we distribute we can get what is wanted:
P*2V = n*R*2T
Which then shows that pressure would stay constant if temperature and volume were to both double.