According to the law of reflection

The angle of incidence = Angle of reflection

Let’s draw a figure for this question –

According to the given question, incident ray is making an angle of 30⁰ with the plane mirror ()

So angle of incidence ∠i + 30⁰ = 90⁰

Angle of incidence ∠i = 60⁰

From law of reflection, Angle of reflection ∠r = 60⁰