Implied expected return rate for 3 Stage DDM

Do we need to know how to do this? Does anyone know the algebraic formula for the 2 Stage? I do not want to have to waste time guestimating come exam day. Can’t seem to find it on the net, either.

Unlikely to be tested as you have to guess and test. No way to plug in values. I can’t imagine they would make you do that with pencil and paper.