Since 68% of the sample ranges from the plus minus first standard deviation from the mean, then interval wherein it will occur will be between 53.5% to 60.5%. I got this answer through adding and subtracting one standard deviation (3.5) from the mean (which is 57).
Circumference of a circle = 2πr
C = 2π(4)
C = 8π
C = 8 * 3.14 = 25.12
In short, Your Answer would be 25.12
Hope this helps!
Consider, pls, this solution.
Note, that V1 marked with orange lines (see the graph), V2 - with green colour.