Kinematics

You drive on Interstate 10 from San Antonio to Houston, one-half the time at 35.0 mi/h (= 56.3 km/h) and the other half at 55.0 mi/h (= 88.5 km/h).
On the way back you travel one-half the distance at 35.0 mi/h and the other half at 55.0 mi/h. What is your average speed
(a) from San Antonio to Houston?
(b) from Houston back to San Antonio?
and
 (c) for the entire trip?