This can be solved using Dalton's Law of Partial pressures. This law states that the total pressure exerted by a gas mixture is equal to the sum of the partial pressure of each gas in the mixture as if it exist alone in a container. In order to solve, we need the partial pressures of the gases given. Calculations are as follows:
P = P1 + P2 + P3
378 kPa= 212 kPa + 101 kPa + P(H2)
P(H2) = 65 kPa
