As I am reading the problem, I see they gave you two pressures, one volume and they are asking for another volume. this should give you a hint that you need to use the following formula.
P1V1= P2V2
P1= 1.00 atm
V1= 0.50 ft³
P2= 3.00 atm
V2= ?
Now we plug the values
(1.00 x 0.50)= (3.00 x V2)
V2= 0.17 ft³
