Well after you subtract A from both sides the equation becomes V-A=Prh+h. So in order to isolate the h you first need to factor it out of the two different h terms that you have and then divide.
V-A=Prh+h V-A=h(Pr+1)
then divide both sides by Pr+1 to find the value of h,
V-A=h(Pr+1) V-A/Pr+1=h.
The problem with what you did was that after subtracting A from both sides you divided by Pr which wouldn't give you the equation 2h=V-A/Pr, instead the equation would become V-A/Pr=h+h/Pr which wouldn't help you at all really. That's why you need to factor first in order to consolidate the h variables and then divide by it's coefficient.
+22 
