The net force on the block parallel to the incline is
∑ F = -mg sin(θ) = ma
where m is the mass of the block, g = 9.8 m/s² is the acceleration due to gravity, θ is the angle the incline makes with the horizontal, and a is the acceleration of the block. Solving for a gives
a = -g sin(θ)
so the block would slide down the incline with acceleration
a = - (9.8 m/s²) sin(30°) = -4.9 m/s²
