Answer
$m = 5.97\times 10^{5}~kg$
Work Step by Step
In part (a), we found that the required positive charge on each object is $q = 5.72\times 10^{13}~C$
We can find the number of protons required:
$\frac{5.72\times 10^{13}~C}{1.6\times 10^{-19}~C} = 3.575\times 10^{32}$
We can find the mass of this number of protons:
$m = (3.575\times 10^{32})(1.67\times 10^{-27}~kg) = 5.97\times 10^{5}~kg$
