In part a., solve for the case when the pendulum is at its maximum height where there is only potential energy. You just need to find the height in terms of r and theta.
In part b., solve for the potential energy first in terms of the height and then since you know that energy is conserved, subtract your answer for the PE off from the total energy E. Once you have the KE, you can solve directly for v from the definition of kinetic energy.