The cool thing about gases is that you can use partial pressure (at constant volume) as a surrogate for moles (Avogadro's Law). Your reaction says that you need two moles of H2 for every mole of CO2, so you need twice the partial pressure of H2 to react stoichiometrically with CO2. Since you are given 300:391 instead of 1:2 (CO2:H2) , the hydrogen is clearly the limiting reactant.
Now it's a stoichiometric problem with the amount of hydrogen determining how much of everything involved is used up or produced.
You can find the moles of hydrogen using the Partial Pressure Ideal Gas Law: PiV = niRT which works because ideal gases essentially act like the other gas isn't there and the partial pressure is the pressure that it would have if it was by itself.
Solve for nH2 by subbing in PH2 in the appropriate atm units P in mmHg/ (760 mmHg/atm) and R =.0821. The Temperature and Volume are given.
Once you have moles of H2 you can find moles of methanol and then gram s of methanol using the reaction coefficients and the molar mass of methanol.