Complex Number question bank (Maths)

Let $z$ be a complex number such that $|z-6|=5$ and $|z+2-6 i|=5$. Then the value of $z^{3}+3 z^{2}-15 z+141$ is equal to

If the locus of $z \in \mathrm{C}$, such that
$\operatorname{Re}\left(\frac{z-1}{2 z+\mathrm{i}}\right)+\operatorname{Re}\left(\frac{\bar{z}-1}{2 \bar{z}-\mathrm{i}}\right)=2$
is a circle of radius $r$ and center $(a, b)$ then $\frac{15 a b}{r^2}$ is equal to :