first to find average age add all the ages divide by number of ages 4
5+4=9
9+6=15
15+39=54
54/4=13.5
For standard deviation find the mean/average
13.5
then subtract the mean from each number/age
5-13.5=-8.5
4-13.5=-9.5
6-13.5=-7.5
39-13.5=25.5
then square each number
-8.5^2=-72.25
-9.5^2=-90.25
-7.5^2=-56.25
25.5^2=650.25
then find the mean/average of the new numbers
-72.25+-90.25+-56.25+650.25=431.5
431.5/4=107.85
then take the square root of the new mean/average