Answer
Please see the work below.
Work Step by Step
The mass of the planet Pluto can be calculated using Kepler's third law:
$T=\frac{2\pi}{\sqrt{GM}}r^{\frac{3}{2}}$ where $G=6.67\times 10^{-11}N.m^2/Kg^2$.
Thus, knowing the approximate value of $r$, we measure the time period of orbit of Charon and in this way $M$ (the mass of Pluto) can be calculated.
