The perimeter of a regular pentagon is 31 cm. find the length of each side.

Regular pentagon is polygon with 5 equal sides, so it is equilateral
let each and every side be x
then perimeter = sum of all sides
                         =x+x+x+x+x
                         5x =31 divide both sides by 5 
                     
                  so x =6.2
this implies each side is 6.2 cm

What mathematical statement is missing ? ? the answer is b