Answer
12.35 years. This value is lower than 1 and more than 3 other data from other exercises, so seems to be good.
Work Step by Step
By using the values from the picture and the given formula:
$s=\sqrt {\frac{n\cdot[\sum(f\cdot x^2)]-[\sum (f\cdot x)^2]}{n\cdot(n-1)}}=\sqrt {\frac{82\cdot 117690.5-2939^2}{82\cdot 81}}=12.35 \ years.$ This value is lower than 1 and more than 3 other data from other exercises, so seems to be good.
