400
A car dealership sold 78 new cars and 67 used cars this year. The number of new cars sold by the dealership increased by 6 cars each year. The number of used cars sold by the dealership has been decreasing by 4 cars each year. If these trends continue, in how many years will the number of new cars sold be twice the number of used cars sold?
What is 78+67=2(67+-4x)
x=4