Since Circumference is

So to get Area, you have to get the radius first:

, which is

Next we divide both sides by

to get:

Now we have to get the area which is

Plug in 15 for r, you should get
Final Answer:
tan x = opposite / adjacent
tan x = 6 / 11
tan x = 6 / 11
x = 28.61 (or 29 degrees rounding to the nearest whole degree)