What do you mean by this question?
20/4 = 5
$5 is the cost of 1 shirt.
You’ll have to adjust the plotting a bit to fit your graph that you have, but this is the main idea.
If it were a complete circle, its circumference would be
(π) x (diameter) = (π) x (2R) = 70 π inches .
Since it's only half of the circle, the length of the curved part is
70 π / 2 = 35 π = <em>109.9 inches</em> .