The Virgo Galaxy Cluster has a mass of $10^{14} M_{\odot}$ and its centre is $16Mpc$ from Earth. The large elliptical galaxy $M87$ lies at the centre of the Virgo cluster. $M87$ has a supermassive black hole at it's centre with an estimated mass of $6 \times 10^9 M_{\odot}$. Take Hubble's constant to be $H_0=70 km s^{-1} Mpc^{-1}$.
Taking the Virgo cluster to be spherically symmetric with a radial density profile given by
$\rho(r)=\rho_0 (\frac{r}{1Mpc})^{-2}$,
Determine the value of the constant $\rho_0$ is S.I units assuming the radius of the Virgo cluster is 1Mpc.
I am confused with how to approach this question, I know that density $\rho=\frac{M}{\frac{4}{3} \pi r^3}$, when I substitute it into the given radial density profile, the $r$ variable doesn't cancel, should I substitute the radius of the cluster into $r$? Is it really that straight forward?