I've tried this problem a few times, but all my attempts have led to dead ends.

Let C be the circle with center -3i and radius 2. The Mobius Transformation R given by the equation \(R(z)=\dfrac{b}{z+d}\) maps C to the Unit Circle in such a way that the inside of C maps to the outside of the unit circle. Find \(|R(1-2i)|\).