Need help calculating chemistry problem

A certain anesthetic contains 64.9% C, 13.5% H, and 21.6% O by mass. At 120 degrees C and 750mmHg, 1.00L of the gaseous compound weighs 2.30 grams. What is the molecular formula of the compound?

Can you show me how to set it up

Take a hypothetical sample of 100 grams.

(64.9 g) / (12.0108 g C/mol) = 5.40347021 moles
(13.5 g) / (1.0079 g H/mol) = 13.3941859 moles
(21.6 g) / (15.9994 g O/mol) = 1.35005063 moles
Divide by the smallest number of moles:
5.40347021 / 1.35005063 = 4.00242042
13.3941859 / 1.35005063 = 9.9212471
1.35005063 / 1.35005063 = 1.00000000
Round to the nearest integer to find the empirical formula:
C4H10O

120 °C = 393.15 °K
PV = nRT
n = PV/RT = (750mmHg) (1.00 L) / (62.36367 L mmHg /K   mol) (393.15 K) =
0.030589 mole
(2.30 g) / (0.030589 mole) = 75.2 g/mole
The molecular mass of C4H10O is 74.1220 g/mol, so that is the molecular formula as well.
The anesthetic with that formula is diethyl ether.

A certain anesthetic contains 64.9% C, 13.5% H, and 21.6% O by mass.
OK, assume as a basis for calculation that you have 1000 g of it
You have 649 g C, 135 g H, 216 g O
Convert to moles
649/12 = 54 mol C, 135 mol H, 13.5 mol O
Double that since 13.5 mol O is ugly
104 mol C 270 mol H 27 mol O
C104H270O27 is your beginning formula


At 120 degrees C and 750mmHg, 1.00L of the gaseous compound weighs 2.30 grams.
THis tells you the molar mass - assume it is an ideal gas, PV = nRT ---> n = PV/RT
Since you know it is 2.3 g, and can find n, you have molar mass.
Tweak the beginning formula, ie, multiply or [more likely] divide each atom's coefficient by the same number to get the same molar mass