X-ray and visible light travel at the same speed in a vacuum. Do they travel at the same speed in the glass?

charge on electron is $e=1.6\times {10}^{-19} \mathrm{C}$, Plank's constant $h=6.626\times {10}^{-34} \mathrm{J} {\mathrm{Hz}}^{-1}$, speed of light $c=3\times {10}^8 {\mathrm{ms}}^{-1}$.

In the figure, the $X$ rays shown are produced when $35.0 \mathrm{keV}$ electrons strike a molybdenum $(Z=42)$ target. If the accelerating potential is maintained at this value, but a silver $(Z=47)$ target is used instead, what values of $\left(\mathrm{a}\right)$ ${\lambda }_{\min }$, $\left(\mathrm{b}\right)$ the wavelength of the $K_{\mathrm{\alpha }}$ line and $\left(\mathrm{c}\right)$ the wavelength of the $K_{\mathrm{\beta }}$ line result? The $K, L$ and $M$ atomic $X$-ray levels for silver are $25.51, 3.56$ and $0.53 \mathrm{keV}$.