Boundary Values & Fourier Series · Medium problem

A rod $0 \le x \le \pi$ with both ends insulated, $u_x(0, t) = u_x(\pi, t) = 0$, obeys $u_t = u_{xx}$ and starts at $u(x, 0) = 2 + \cos 2x$. Find the temperature at the left end at time $t = \dfrac{\ln 3}{4}$.