That is a good example where 'a lot of steps' is very helpful.  The denominator 'a' is eliminated by multiplying both sides by 'a' (cancels the 'a' in the denominator of the left side and multiplies 'a' times 'b' on the right side).  That leaves adding 'a' to both sides of the equation, eliminating 'a' on the left side and adding 'a' to the right side.