Of moles of O2... V= 50 mL P= 1.5atm T= 25oC?

Calculate the number of moles of oxygen gas as it is collected into a flask whose volume is 50.0 mL. The pressure inside the flask 1.5 atm and the temperature is 25 oC. i need the step by step solution and an example would be AWESOME i give props to ths\ose of u who understand this stuff hahah :) thank U!!