[tex]W=2 \dfrac{PR}{R} -r[/tex]
[tex]W=\dfrac{2PR}{R} -r[/tex]
[tex]W+r= \dfrac{2PR}{R} [/tex] [tex]Add \ r \ to \ both \ sides[/tex]
[tex](W+r)R=2PR[/tex] [tex]Multiply \ both \ sides \ by \ R[/tex]
[tex]R= \dfrac{2PR}{W+R} [/tex] [tex]Divide \ both \ sides \ by \ W+r[/tex]
