Let $z = 2 e^{10 \pi i/21} $ and $w = e^{\pi i/7}$. Then if $[(z-w)^6 = r e^{i\theta}]$where $r \geq 0$ and $0 \leq \theta < 2\pi$, what is the ordered pair $(r, \theta)$?

I have the starting idea of drawing it out on the graph table. Currently, I need some help with the algebraic portion of the problem.