HELP on SAT Math Question?

There is this question on the SAT (also on PSAT) where there are 2 circles next to each other and a tzoid. The bottom corner of the tzoid goes into the centers of the circles. your told that the radius of the circle (which is also half the bottom base) is equal to 4 and you need to find teh perimiter. Can anyone tell me how to do it? Picture at http://img221.imageshack.us/img221/2406/55371031nt4.jpg