cyclopropane

[logistic_guy]

here is the question

Cyclopropane, a gas used with oxygen as a general anesthetic, is composed of $\displaystyle 85.7\%$ C and $\displaystyle 14.3\%$ H by mass. (a) If $\displaystyle 1.56$ g of cyclopropane has a volume of $\displaystyle 1.00$ L at $\displaystyle 0.984$ atm and $\displaystyle 50.0^{\circ}C$, what is the molecular formula of cyclopropane? (b) Judging from its molecular formula, would you expect cyclopropane to deviate more or less than Ar from ideal-gas behavior at moderately high pressures and room temperature? Explain. (c) Would cyclopropane effuse through a pinhole faster or more slowly than methane, CH$\displaystyle 4$?


my attemb
i understand the main ingredients in this question is carbon and hydrogen and argon
i know also $\displaystyle 1$ carbon atom with $\displaystyle 4$ hydrogen atom give the compound "methane" CH$\displaystyle 4$
reactions is my game but i'm a little confused here
it's not easy to determine the molecular formula of cycloprpane without knwoing the atmic mass of carbon and hydrogen
i think i can find them in the periodic table but then how to calculate the number of moles?