The average speed is (distance covered) / (time to cover the distance) .
For example:
The average speed for the 'car' part of her trip is
(distance covered in the car) / (time in the car) =
(120 km) / (3 hours) = 40 km per hr.
Answering the question:
Average speed for the whole journey is
(distance covered on the journey) / (time spent on the whole journey) =
(240 + 120 + 3) km / (4 + 3 + 1/2) hours =
363 km / 7.5 hours = 48.4 km per hour
Good luck on the test !
