N = normal force by the surface of incline on the box resting on it
m = mass of the box resting on the incline surface = 30 kg
g = acceleration due to gravity acting on the box = 9.8 m/s²
θ = angle of the incline with the horizontal surface = 15⁰
from the force diagram , force equation perpendicular to incline surface is given as
N = m g Cosθ
inserting the values in the above equation
N = (30 kg) (9.8 m/s²) Cos15
N = 284 newton
