19.1 inches. I hope this helps you!
It can be made 1/10 as much by moving it one place to the right.
The formula for finding area of a circle is

.
Essentially, we have two circles here. One is a larger outer circle, and the other in a smaller inner circle. In order to find the area of the sidewalk, we must find the area of the outer circle, then find the are of the inner circle. After we find both areas, we subtract.
See attached image for process of finding area, and subtracting areas to find the final area of the sidewalk.
See picture reply for answer.
2,380 m^
Ratio of the sides 14/36 = 7/18
Ratio of the area is the ratio of the sides squared (7/8)^=49/324
49/324 = 360/A
A= 360*324 divided by 49 = 2,380.4081