You can solve this problem and calculate the arc lenght, by applying the following formula:
s=θr
s: it is the arc lenght.
θ: it is the central angle (θ=2π/3).
r: it is the radius of the circle (r=10 inches).
When you substitute these values into the formula, you obtain the arc lenght (s):
s=θr
s=(2π/3)(10)
Then, you have that the value of the arc lenght is:
s=20.94 inches