7. Two thin conducting half plane, at $\phi = 0$ and $\phi = \frac{\pi}{6}$, are insulated from each other along the z axis. Given that the potential function $0 \leq \phi \leq \frac{\pi}{6}$ for $V = -\frac{60\phi}{\pi} V$, find the energy stored between the half planes for $0.1 \leq r \leq 0.6$ m and $0 \leq z \leq 1$ m. Assume free space.