Which formula using letters could relate the lengths of side with the perimeter?

The formula that relates the lengths of the sides of a polygon to its perimeter is given by ( P = a + b + c + \ldots ), where ( P ) represents the perimeter and ( a, b, c, \ldots ) represent the lengths of the individual sides. For a triangle, for example, the perimeter can be expressed as ( P = a + b + c ), where ( a, b, ) and ( c ) are the lengths of the triangle's sides.