Three gases, methane, xenon, and oxygen are confined in a 5.0 L vessel at a pressure of 15.0 atm. Intially the vessel contains 3.0 moles of methane, 3.0 moles of xenon, and 4.0 moles of oxygen. What would the partial pressure of methane be if 2.0 moles of methane are added to the vessel? Assume that the volume and temperature of the vessel remain constant.