The New Gotham Department of Transit is taking an inventory of its vehicles. There are three times as many buses as train cars. 20 percent of the buses are powered by alternative fuels, of which 40 percent are powered by biofuels, 20 percent by hydrogen, and the remainder by natural gas. 25 percent of train cars are less than 5 years old, which is half the rate for natural gas buses. What percentage of New Gotham’s vehicles are natural gas buses that are at least 5 years old?