What is the difference between the mean and the median of the data set?
{22, 8, 10,18,12, 20}

Let's sort first,

8, 10, 12, 18, 20, 22

We can quickly add these up as 8+22 + 10+20 + 12+18 = 3(30) = 90

so the mean is 90/6 = 15

The median is the middle one.  We have six so we take the average of the two middle ones,

median = (12+18)/2 = 15

That's the same as the mean.

Difference is zero

the arc length is found by finding the circumference of the full circle (2xpixradius) and then dividing by 4 to find just one quarter of the circle (90 degrees).