Lenore drove 200km. For the first 100km of the trip, she drove at a speed of 40 km/h. For the second half of the trip, she traveled at a speed of 60 km/h. What was the average speed of the entire trip?

MY WORK:

I know we can use R = D/t

I first need to find the time.

T = D/R

T = 100/40

T = 2.5 hours

I then did the same thing for the second part of the trip.

T = 100/60

T = 1.7 hours

This is where I get stuck.