Sulfur dioxide may be converted to SO3, which has many uses. A gas stream that has a composition of 10% SO2, 9% O2, and 81% N2 is to be passed through two reactor stages. The reaction conversion of the SO2 to SO3 in the first stage is 0.75 and in the second stage is 0.65. In order to boost the overall conversion to 0.95, some of the exit gas from the second reactor is recycled back and mixed with the inlet gas to the second reactor. If 100 moles are in the feed to the entire system, how many moles are in the recycle stream