Given open$-$loop transfer function $KG(s)=\frac{K(s^2+6s+10)}{(s+1)(s+4)}$ and a unity feedback system for questions $6$ and $7($Note: $\frac{dK}{ds}=0$@$-2\mathrm{.}838,-9\mathrm{.}162)$

The angle of arrival to the complex open loop zero is degrees $($please specify which zero you use to calculate this value$).$