Chemistry
posted by Hannah .
The vapor pressure of diethyl ether is 463.57 mm Hg at 25 degrees celsius. How many grams of aspirin C9H8O4, a non volatile nonelectrolyte (mw=180.1g/mol), must be added to 216.7g of ether to reduce the vapor pressure to 453.74 mm Hg.
Ether=74.12g/mol
This question is similar to the other one that I posted. Do I first have to convert to moles for both?

Yes for ether. You don't know grams aspirin so you can't calculate moles aspirin.
Subtract normal vp ether  vp ether desired, plug into
pether = Xether*Po ether and solve for Xether.
Then find Xaspirin (it's 1.000  Xether) and from that grams aspirin.
It's just the reverse of what you did in the other problem. 
so I did 463.57  453.74 = 7.600
Then I found moles of ether to be 4.0313.
I do not understand the next step to find Xether.