A car moves in a straight line at 16.0 m/s for 10.0 miles, then at 30.0 m/s for another 10.0 miles.

For the first part of the trip:

the car moves at 16 m/sec for 10 miles (which is 16093.44 meters)

velocity = distance / time

time1 = distance / velocity = 16093.44 / 16 = 1005.84 seconds

For the second part of the trip:

the car moves at 30 m/sec for another 10 miles (which is 16093.44 meters)

velocity = distance / time

time2 = distance / velocity = 16093.44 / 30 = 536.448 seconds

For the total trip:

total distance is 20 miles (which is 32186.88 meters)

total time = 1005.84 + 536.448 = 1542.288 seconds

average velocity = total distance / total time = 32186.88 / 1542.288

= 20.869 meters/second