Answer
$1.62\times10^{-25}kg$. This is about 97 proton masses.
Work Step by Step
Table 44.1 gives the mass of the $Z^0$ in energy units, $91.2 GeV/c^2$.
$$91.2\times10^9\;eV \frac{1.602\times10^{-19}J}{eV}=1.461\times10^{-8}J$$
This is the value of $mc^2$, where m is the mass in kilograms.
Divide by the mass of the proton to find the mass ratio of 97.