Answer
$1\times10^{6} \text{ g/cm}^{3}$
Work Step by Step
mass = $2\times10^{36}$ kg = $2\times10^{39}$ g
radius = $7.0\times10^{5}$ km = $7.0\times10^{10}$ cm
volume = $\frac{4}{3}\times3.14\times(7.0\times10^{10})^{3}$
volume = $1.4\times10^{33}\text{ cm}^3$
density = $\frac{mass}{volume}$
=> density = $\frac{2\times10^{39}}{1.4\times10^{33}}$
=> density = $1\times10^{6} \text{ g/cm} ^{3}$
