In this question I would initially aim to get an a on both sides of the equation. My first step would be to multiply both sides by (4-a) to do this. After this point I would expand out the brackets on the left hand side, this would allow me to get 4p - ap on one side. The next step is then to get the term you want as the subject on one side. Therefore I would subject 5 and add pa to both sides. This would then allow me to have 3a + pa on the left hand side. Once I have done this I can see that the left hand side both terms have a common factor of a, therefore the next step is to factor that a out on the left hand side to get a(3+p). Finally I can now divide both sides by (3+p) to get a as the subject.