We have to apply the trigonometric formula:
Cos b = adjacent side / hypotenuse
Where b is the angle ( 30), adjacent side is AY (missing side) and the hypotenuse is RY=48 cm.
Replacing:
Cos 30 = AY / 48
Solve for AY
AY = Cos 30° (48)
AY = 41.57 cm = 24 √3 cm