We know the formula for arc length is
s = r theta were r is the radius and theta is the central angle in radians
Changing 40 degrees to radians
40 * pi/180 = 2pi/9
Using the formula for arc length we can find the radius
3 pi /2 = r * 2pi/9
Solving for r
3 pi/2 * 9/2pi = r
27/4 = r
We want to find the circumference
C = 2 * pi * r
C = 2 * pi * 27/4
C = 27 pi/2 inches
Answer 27pi/2 inches