Answer
The partial pressure of the helium is $10.7 atm$
Work Step by Step
We can find the partial pressure by using Dalton's Law of Partial Pressures which states the total pressure of a mixture of gases is simply the summation of the partial pressure of the gases;
If the total pressure is $11.0 atm$ and the partial pressure of the oxygen gas is $0.30 atm$, the partial pressure of the helium gas is $11-0.3 = 10.7$ atm because $0.3 + 10.7 = 11.0$ atm.