I am working on a calculus homework problem that i am stuck on. It is a rate of change problem A train travels from city A to city B and then to city...

I am working on a calculus homework problem that i am stuck on. It is a rate of change problem

A train travels from city A to city B and then to city C. The distance from A to B is 120 miles and the distance from B to C is 337.5 miles. The average speed from A to B was 60 miles per hour, and the average speed from B to C was 75 mph. What was the average speed from A to C (that is for the entire trip) in miles per hour?