Explanation:
imagine the triangle is rotated and twisted so that the vertex with the 60° angle is the bottom left vertex and therefore the center of the trigonometric circle around the triangle.
so, y is the radius of that circle.
4 = sin(60)×y
x = cos(60)×y
sin(60) = sqrt(3)/2
cos(60) = 1/2
y = 4/sin(60) = 4 / sqrt(3)/2 = 8/sqrt(3)
x = cos(60)× 8/sqrt(3) = 1/2 × 8/sqrt(3) = 4/sqrt(3)