Maths help plzzzzzzzzzzzzzzzzzzzz

A school has 20 teachers. one of the teacher retires at the age of 60 years and a new teacher replaces him. this reduces the average age of the staff by 2 yrs. then the age of new teacher is?

we will call the group of the other 19 teachers = x

(x + 60) / 20 = average (which we will call y)

so
(x + 60) / 20 = y

call the new teacher z
(x + z) / 20 = y - 2
x + z = 20y - 40

x + 60 = 20y
x + z + 40 = 20y

so for
x + 60 = 20y
and
x + z + 40 = 20y
then
z + 40 = 60

60 = z + 40
20 = z

the new teacher is twenty years old

you have to know the average ages of the other teachers to calculate.
Otherwise you cannot know the age of the new teacher though you could probably express it as a variable in a equation.

missing information

not enough info to complete

x + 60 = 20y
x + z + 40 = 20y

x + 60 = x + z + 40
x + 60 - x - 40 = z
20 = z

z = 20

Need more info