A vessel of volume V = 7.5 1 contains a mixture of ideal gases at a temperature

Question:

A vessel of volume V = 7.5 1 contains a mixture of ideal gases at a temperature T = 300 K: v1 = 0.10 mole of oxygen, v2 = 0.20 mole of nitrogen, and v3 = 0.30 mole of carbon dioxide. Assuming the gases to be ideal, find:
(a) The pressure of the mixture;
(b) The mean molar mass M of the given mixture which enters its equation of state pV = (m/M) .RT, where m is the mass of the mixture.