rotate object around a point over time

I would like to Rotate an Object A with a set Distance around a point B. The collision gives me the information how many degrees it will have to turn in a Vector3 param. The radius would always be the same.
Maybe im just not getting it right but i somehow cant get it done properly.
Thanks for any help in advance.

The most obvious way to be R away from a point at angle A is:

Vector3 fwdR = new Vector3(0,0,R);

If says to start at the center point, take a forward line, spin it by A degrees, and move that much away. As A changes, you keep spinning.