Answer
$E_{gap} = 4.20 eV$
Work Step by Step
The width of band gap is the same as energy of photon with wavelength 295 nm. So,
$E_{gap} = \frac{hc}{\lambda}$
Where $hc = 1240 eV.nm$
and $ \lambda = 295 nm$
$E_{gap} = \frac{1240 eV.nm}{295 nm}$
$E_{gap} = 4.20 eV$
