Drop a line from the apex of the triangle to form 2 triangles then use law of sines:
Sin30 / height = sin 90 / 4
4 sin 30 = height = 2
sin 60 / base = sin 90 / 4
4 sin 60 = base = 2 sqrt 3
area of each triangle = 1/2 base * height
1/2 (2) * 2 sqrt 3 = 2 sqrt 3 for each triangle (remember, there are two) Area = 4 sqrt 3