Answer
$1.1\times10^{-34}\,m$
Since wavelength is small and can be neglected, wave nature of matter is not important for a baseball.
Work Step by Step
Recall that de Broglie wavelength is $\lambda=\frac{h}{mv}$ where $h$ is the Planck's constant, $m$ is the mass and $v$ is the velocity.
$m=143\,g=0.143\,kg$
$v=95\,mi/h=95\,mi/h\times\frac{1609.344\,m}{1\,mi}\times\frac{1\,h}{3600\,s}$
$=42.4688\,m/s$
Substituting values, we have
$ \lambda=\frac{6.626\times10^{-34}\,J\cdot s}{(0.143\,kg)(42.4688\,m/s)}$
$=1.1\times10^{-34}\,m$
Since wavelength is small and can be neglected, wave nature of matter is not important for a baseball.
