Assume that energy losses (due to aerodynamic resistance or bearing friction are negligible).
At the highest point, the pendulum has its maximum potential energy (PE) and zero kinetic energy (KE). The total energy is equal to the PE = 141 J.
At the lowest point, the pendulum has its maximum KE, and zero PE. The total energy is equal to the KE.
Because energy is preserved, therefore
KE at the lowest point = PE at the highest point = 141 J.
Answer: 141 J