In a class with a certain number of students if a teacher weighing 78 kg is added, then the average weight of class is increased by 2 kg. If one more teacher weighing 66 kg is added, then the average weight of the class increases by 3.5 kg over the original average. What is the original average weight (in kg) of the class?
1
25 kg
2
22 kg
3
16 kg
4
18 kg
5
24 kg