Apendulum has 409 j of potential energy at the highest point of its swing. how much kinetic energy will it have at the bottom of its swing? joules

According to law of conservation of energy, 
Energy can neither be constructed nor be destroyed but can be transformed from one form to another.

At the highest point of the pendulum(point b), pendulum is associated with potential energy only and no kinetic energy.
Therefore total energy at point b = potential energy = 409 J.... i

At the bottom most point(point a), pendulum is associated only with kinetic energy and no potential energy.
Therefore total energy at point a = kinetic energy ---- ii
From i and ii,
Kinetic energy = potential energy = 409 J.(Conserving energy)

Hence kinetic energy at the bottom most point is 409 J.
Hope this helps!!