The length of arc is s=rx where x is the angle in radians and r the radius of the circle.
Since no radius has been given the only meaningful measure is the angle itself, 60 degrees. 60 degrees is π/3 radians (approximately 1 because π= about 3.14). So the answer would be sixty degrees of arc.
For an angle of 60 degrees, the length of the arc is approximately the same as the radius of the arc.