Calculating Volume of Helium Balloon at Different Temperatures

[jagged06]

Question from my homework. I'm not exactly sure what I am doing wrong, and it is bugging me. I hope this post is in the right forum.

Imagine that 9.9 g of liquid helium, initially at 4.20 K, evaporate into an empty balloon that is kept at 1.00-atm pressure. What is the volume of the balloon at the following?
(a) 23.0 K (b) 299 K

After missing the question, help was given, but I can't make sense of it:

Apply the ideal-gas law to find the volume of the gas at 4.2 K, and a fixed amount of gas to find its volume at the given temperatures.

 

[m.medhat]

you must have the density at 4.2 the you can calculate the volume at 4.2 . then you can calculate the volume at the other temperatures from the equation
V1/T1=V2/T2=V3/T3=...=Vn/Tn