I am really stuck on a trigonometry problem please help if you can.

---------------------------

A circle has a radius of 'r'

And its center is at 'C'

The distance from 'A' to 'B' is 'x'

find 'r' if

A = 45 degrees and 'x' equals 15

C

-|-\

-|---\

r|-----\r< C to B is r and C to D is also r

-|-------\

-|---------\B< B to A is 15

-|-----------\

-|_____45\x < x equals 15 and 45 is Angle A

D-------------A

Thats how it is put in the book and The answer is 36 but I do not know how to solve this

Because r ends up on both sides of the equation.

if I go

sin45 = r/r+15 I get

(r+15)(sin45) = r

and so on I really could use some help here because I need trig for programming class. thanks