To find the average speed, you need to calculate the total distance traveled and divide it by the total time taken.
The girl walks 7 km in 2 hours and then 5 km in 3 hours, so the total distance traveled is 7 km + 5 km = 12 km.
The total time taken is 2 hours + 3 hours = 5 hours.
To find the average speed, divide the total distance by the total time:
Average Speed = Total Distance / Total Time = 12 km / 5 hours = 2.4 km/h
Therefore, the girl's average speed is 2.4 km/h.