for example if a golem use earthquake the power will be 150 since both golem and earthquake is ground type,
but if you use it on for example a pikachu will the power be 300 or 250 then?
All boni are multiplied.
Base power STAB type effectiveness
In case of a super effective STAB earthquake:
100 1.5 (STAB) 2 (effectiveness) = 300