MEC charter a bus which holds at most 45 people to go to an educational tour in a museum. The bus company requires at least 30 people to go. It charges 223 R.O. per person if up to 40 people go. If more than 40 people go, it charges each person 223 R.O. less 0.2 times the number more than 40 who go.

Find the total cost as a function of the number of students who go.