The angle across from the 5cm side is 30°
In a 30-60-90 triangle like this, the side opposite the 60° will be √3 times as long as the side opposite the 30° angle
So BC = height of the triangle = 5√3
So....the area = (1/2) base * height = (1/2) (5) (5√3) =
(25/2)* √3 cm^2 ⇒ 21.7 cm^2