Mean = sum of all values / no. Of values
I am also considering mean Anita's Age in Calculating Mean.
Let the age of Anita and others is a, b, c, d,e,f respectively !
Now Mean of their age =(a + b + c + d + e + f) / 6 = 6 years
from here ,, a + b + c + d + e + f = 36 years
after 10 years anita and all other ages will be +10 years
Mean Age after 10 years
mean age = { (a+10)+(b+10)+(c+10)+(d+10)+(e+10)+(f+10)} / 6
= {(a+ b +c + d + e + f) +(10+10+10+10+10+10)} / 6
= (36 + 60) / 6
= 96/6 = 16 years
similarly age after 20 years can be calculated !