Chem HW question im really stuck please help - pressure and amount of mass formed?

Question

A mixture of N2(g) and O2(g) occupies 10 L at 250 K and 8000 mm Hg. All of the O2(g) is removed as P4O10(s) by reaction with P4(s) and the remaining N2(g) has a pressure of 250 mm Hg at 250 K. What mass of P4O10(s) is formed?

Answer 1

Use pV = nRT. n is what you are after.

p = 8,000-250 (convert to Pa).
V = 10 litres (convert to cubic metres).
T = 250K.