In 2007, the county authorized EnviroCAB, a new taxi company, to operate exclusively with a hybrid electric vehicle fleet of 50 vehicles and also issued permits for existing companies to add 35 hybrid cabs to their fleets. As operations began in 2008, EnvironCab became the first all-hybrid taxicab fleet in the United States and the company not only offset the emissions generated by its fleet of hybrids, but also the equivalent emissions of 100 non-hybrid taxis in service in the metropolitan area. The Green transport taxi expansion was part of a county campaign known as Fresh AIRE, or Arlington Initiative to Reduce Emissions, that aimed to cut production of greenhouse gases from county buildings and vehicles by 10 percent by 2012. Arlington has a higher than average percentage of households without a car. In 2015, 13.4 percent of Arlington households lacked a car, and dropped slightly to 12.7 percent in 2016. The national average is 8.7 percent in 2016. Arlington averaged 1.40 cars per household in 2016, compared to a national average of 1.8.
Question: How many more hybrid electric vehicles was EnviroCAB authorized to have than existing companies?
Answer: 15