The average age of a class of 39 students is 15 years. If the age of the teacher is included, then the average increases by 3 months. Find the age of the teacher.

Answer: Option B

Average age of the class = 15 years
Average age of the class including teacher = 15 years 3 months
Teacher's age
= 15 × 40 + $$\frac{3}{12}$$ × 40 - 15 × 39
= 610 - 585
= 25 years