Mass and mole fraction of Helium in Ideal gas problem

[TLeo198]

Problem:  A certain mixture of He and Ne in a 356-cm^3 bulb weighs 0.1480 g and is at 20 degrees C and 748 torr.  Find the mass and mole fraction of He present.

Attempt:  OK, so I figured that I had to use the ideal gas law equation of state, PV=nRT, with R = 0.0821 L*atm/mol*K.  I changed the units of volume, temperature, and pressure to .356 L, 293 K, and 0.984 atm respectively.  Doing a simple plug and chug, I found the # mol (n) to be 0.0146 mol.  This is where I get stuck.  It says to find the mass fraction and mole fraction of He.  I think I got the mass fraction, which I just took the mol (n) I found and multiplied it by the molar mass of He to find .0584 g of He.  I then took that and divided by .1480 grams to find the mass fraction of the He.  I don't know if that was correct, and have no idea how to find the moles of He.  Any help is greatly appreciated!

[Borek]

You have two unknowns - n_Ne and n_He. Try to write two equations - one for total number of moles, one for total mass.