Answer
$4.05\times10^{14} ~kg$
Work Step by Step
The radius of a proton is $5\times10^{-16} ~m$
The volume of a proton is $\frac{4}{3}\pi r^3 = 5.24\times10^{-46} ~m^3$
The density of a proton is $\frac{mass}{volume} = \frac{10^{-27}~kg}{5.24\times10^{-46} ~m^3} = 1.91\times 10^{18} ~\frac{kg}{m^3}$
The radius of the baseball is $\frac{0.23 ~m}{2\pi} = 0.037 ~m$
The volume of a baseball is $\frac{4}{3}\pi r^3 = 2.12\times10^{-4} ~m^3$
If the baseball had the same density as a proton, the baseball's mass would be: $(2.12\times10^{-4} ~m^3)( 1.91\times 10^{18} ~\frac{kg}{m^3}) = 4.05\times10^{14} ~kg$
