Please reason step by step, and put your final answer within \boxed{}.
Xiao Ming departs from his home to his grandmother's house on a bicycle at a speed of 12 km/h. After 2.5 hours, his father realizes that Xiao Ming forgot to bring his homework and starts chasing him on a motorcycle at a speed of 36 km/h. Half an hour after Xiao Ming reaches his grandmother's house, his father arrives. What is the distance between Xiao Ming's home and his grandmother's house in kilometers?
user