VS 2012 [Help] How Can i get a "Char" position(X/Y) in richtextbox?

Hey all..
i am having aproblem with finding a char like a smile ":)" position(x/y) to replace it with a picture box control in a richtextbox..
if anyone can give me a hint or away to do it.. i will be greatly thankful. :(

Thanks in advance for reading. :)