what the hell? help me decipher this chem problem?

Question

Magnesium can be used as a "getter" in evacuated enclosures, to react with the last traces of oxygen. (The magnesium is usually heated by passing an electric current through a wire or ribbon of the metal.) If an enclosure of 0.376 L has a partial pressure of O2 of 3.50 10-6 torr at 26°C, what mass of magnesium will react according to the following equation?

2 Mg(s) + O2(g) 2 MgO(s)

Answer 1

Moles of O2 present

= (3.5x10^-6/760)*0.376/(0.0821*299) = 7.054x10^-11

So, mass of Mg = 2*7.054x10^-11*24 = 3.39 x 10^-9 g