Spur Gear beam strength calculation by using lewi's equation

spur gear is a power transmission system for one shaft to another shaft without sliping. It should be having bending stress at fillet of the spur gear. so how to calculate bending stress for using following equation

where,

          = Bending Stree
                F        = Tancential Force
                y         = Form Factor
                pc       = Pitch Circul Diameter