Remember that the formula for the lenght of an arc is:
[tex]L=2\pi r(\frac{\theta}{360})[/tex]
Notice that the expression
[tex]2\pi r[/tex]
is the circunference of the circle
Using this formula and the data given,
[tex]L=72\cdot(\frac{60}{360})\rightarrow L=12[/tex]
Therefore, the lenght of the arc is 12
