Nitrogen dioxide is one of the many oxides of nitrogen (often collectively called "NOx") that are of interest to atmospheric chemistry. It can react with itself to form another form of NOx, dinitrogen tetroxide. A chemical engineer studying this reaction fills a 25L tank with 11.mol of nitrogen dioxide gas. When the mixture has come to equilibrium she determines that it contains 6.7mol of nitrogen dioxide gas.

The engineer then adds another 3.7mol of nitrogen dioxide, and allows the mixture to come to equilibrium again. Calculate the moles of dinitrogen tetroxide after equilibrium is reached the second time.