Problem Solving

In May,xiang sold 15 used cars.For these 15 cars,the range of selling price was $15000 and lowest selling price was $4500. In june,xiang sold 10 used cars.for these 10 cars, the range of selling prices was $16500 and the lowest selling price was $6100. what was the range of selling prices of the 25 used cars sold by xiang in may and june

answer is 18100..but any method to solve it quickly

Thanks
Gopal