The average age of 20 students in a class is 15 yr. If the teacher's age is included, the average increases by one. What is the teacher's age?

The average age of 36 students in a group is 14 years, when teacher's age is included to it, the average increases by one. What is the teacher's age in years?

The average age of 24 boys and a teacher is 15. When the teacher's age is excluded the average decreases by 1 . What is the age of the teacher ?