How so I figure out this equation? I am studing to go back to school and this is one of the questions I just dont remember how to do.

I have a small circle inside a large circle with space inbetween them. Both circles have the same center, and the radius of the larger circle is R. if the radius of the smaller circle is 3 units less than R, which of the following represents the area of the shaded region (the space inbetween the small and big circle)

answer is: pie signRpower of 2 - pie sign(R-3)power of 2

if you can understand that - please help me do the same. how did that get that and why is it written like that?