Back to the first one - you liked PV = nRT, what variables do you have so far? What are you missing?
For the second one, if t is time, then you are using the wrong equation. Go back and look at Graham's Law of Effusion. (Link shown in previous response). And think about what you are given, and what you are asked for - you are comparing a rate of arsenic sulfide effusion to a rate of argon effusion, you aren't comparing rates of arsenic to rates of sulfide. Arsenic sulfide will effuse as single molecules, not as separate atoms.