3.29: GP common ratio in terms of $k$

A GP has $4$th term $\dfrac{8}{27}k^{6}$ and $6$th term $\dfrac{32}{243}k^{10}$, with $r>0$. Find $r$ in terms of $k$ and the first term.

Given $S_{\infty}=3$, find the possible values of $k$.