Answer :
At constant temperature and moles, the answer can simply becomes P1V1 = P2V2. The original sample is 760 torr and 5.00 l, and was then compressed to 3.00 l. (760 torr)(5.00 l ) = (3.00 l)(X torr), X = 1270 torr. The new pressure exerted by helium on its container is 1270 torr.