Adam and Jacob are driving in opposite directions from the park at $60\textasciitilde km/h$ and $80\textasciitilde km/h$ respectively. Both of them started at the same time. After $3$ hours, Jacob reached home. Adam still had another $30$ minutes before reaching home. How far apart are their home? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle