Brewster’s angle is angle of incidence of light on a refracting surface for which refracted and reflected light are linearly polarised. They are also perpendicular to each other.

According to Brewster’s law when angle of incidence is Brewster angle, say θ_B,

tan(θ_B) = μ

where μ is refractive index of the refracting medium

i.e., tan(θ_B) = 1.5

θ = tan^-1(1.5)

= 56.3°