Be careful of this come exam day... just because a "growth rate" is given in a vignette, that does not mean it's the "sustainable growth rate". Make sure if at all possible to calculate the sustainable growth rate yourself.
Last year on the sample they had a question which gave you a growth rate but also enough information to compute 'g'. If you used the growth rate given it was wrong because this was not the "sustainable" growth rate.
dividend growth rate and earnings growth rate are the same if the dividend payout ratio (or retention ratio) is constant. Generally, if you are using g = ROE*b, you are going to assume that b is constant, hence payouts are constant, hence dividend growth = earnings growth.