$\displaystyle z^4+16=0$. Solve and graph all solutions.

Hint: Then use the solutions to factor $\displaystyle z^4+16=0$ into quadratic factors with real coefficients.

It gave me a hint, but I don't understand this hint.

For me, now I know only $\displaystyle z = -2i$. And after that, I am not sure how to make it in $\displaystyle z=re^{i\theta}$

Would you please tell me the direction.

Thank you.