Question

gmat 数学题目，没有读懂，求翻译和详解

During a trip on an expressway, Don drove a total of x miles. His average speed on a certain 5-mile section of the expressway was 30 miles per hour, and his average speed for the remainder of the trip was 60 miles per hour. His travel time for the x-mile trip was what percent greater than it would have been if he had traveled at a constant rate of 60 miles per hour for the entire trip? 答案：500/x%

Answer 1

一次在高速公路上旅行时，唐驾车开了一共x英里。在某段5英里的路程中他的平均速度是30英里/小时，在剩下的路程中他的平均速度是60英里/小时。同他全程以60英里时速行驶相比，他所花的时间要多出百分之多少？
小学生题目，不需要解释了吧