P(helium) + p(oxygen) = P(total) => P(helium) = P(total) - p(oxygen) = 7 - 0.21 = 6.79 atm Solution P(helium) + p(oxygen) = P(total) => P(helium) = P(total) - p(oxygen) = 7 - 0.21 = 6.79 atm.Read less