Question 958377
You are stuck on something that is not in your way.  You know what to do so just keep going.  


Note this idea, symbolically, very very carefully:
{{{(h+r+s)(h+r-s)}}}
{{{((h+r)+s)((h+r)-s)}}}
{{{(h+r)^2-s^2}}}


In worded description, you should arrange associations to permit easy use of Difference of Squares.