You have the following equation:
1 + sinθ = 1/2
in order to solve the previous equation for θ, proceed as follow:
1 + sinθ = 1/2 subtract 1 both sides
sinθ = 1/2 - 1 simplify right sides
sinθ = -1/2 apply sin⁻¹ both sides to cancel sin left side
sin⁻¹(sinθ) = sin⁻¹(-1/2)
θ = sin⁻¹(-1/2)
θ = -30°
-30° is the same as 360° - 30° = 330°
Hence, the value of θ is 330°