The arc is formed on the circle.
The proportion of the length of the arc, x, to the circumference of the circle will be equal to the proportion of the central angle it faces to 360 degrees. Then, we can write
x 288
------------ = ----------
2*3.14*4 360
360x = 288*2*3.14*4
x = 20.1 units (rounded to the nearest tenth)