10 years a go the average age of all the 25 teachers of the girls college was 45 years. 4 years a go the principal has retired from her post at the age of 60 year. So after one year a new principal whose age was 54 years recruited from outside . The present average age of all the teachers is if principal is also considered as a teacher:

Options

A. `54(18)/(25)` years
B. `55(17)/(25)` years
C. `49(1)/(2)` years
D. none of these