A beam of light both reflects and refracts at the surface between air and glass, as shown

Question:

A beam of light both reflects and refracts at the surface between air and glass, as shown in Figure. If the index of refraction of the glass is ng, find the angle of incidence, 1, in the air that would result in the reflected ray and the refracted ray being perpendicular to eachother.

$A beam of light both reflects and refracts at the$