How exactly is STAB damage calculated?

[RetroTyphlosion]

So, I've been looking at the power of Pokemon attacks, and trying to figure STAB in to it. I have a few questions, and if anyone could answer them that'd be great:
1. Does STAB basically increase the Power of the attack by 50%? For instance, if I was to use Earthquake(which has 100 power), using my Dugtrio, which gains STAB from it, would the Power of Earthquake be 150?

2. How does STAB work with Super-Effectiveness? For instance, let's go back to my Earthquake situation. If Earthquake really does have 150 Power, would Super-Effectiveness be 50% of that, gaining an extra 75 Power for a 225 Power move? Or would it just be 50% of the original 100 again, making it 200 Power? Or am I just doing this wrong?

3.Does STAB nullify Not Very Effectiveness? If a move isn't effective, it drops the Power by 50%, right? And STAB increases the move's Power by 50%, right? So, if I used Earthquake on a Pokemon that was resistant to it, would STAB cancel out the Resistance and make it a regular, 100 Power Earthquake?

If anyone knows the answer to theese questions, please lend a hand and answer them in the commentes below!