The following figure shows the multiple reflections of a light ray along a glass corridor where the walls are either parallel or perpendicular to one another. If the angle of incidence at point $\mathrm{P}$ is $30°$, then the angles of reflection of the light ray at points $\mathrm{Q}$, $\mathrm{R}$, $\mathrm{S}$ and $\mathrm{T}$ respectively are