A membrane-based gas separation unit separates a gas mixture into product stream and reject stream. A gas mixture input is given to the gas membrane separator with 40mol%O2 and 60mol%N2. The reject stream contains 80mol% of the total input moles. The product stream composition is 25mol%O2 and 75mol%N2, what is the percentage of O2 in the reject stream? Select one: a. 0.88 b. 0.44 c. 0.22 d. 0.66