If you don't know trigonometry:
In a 30-60-90 triangle, the length of the side opposite the 30° angle is half the length of the hypotenuse and the length of the side opposite the 60° angle is √3 times as long as the side opposite the 30° angle.
So, since the hypotenuse has length 4, the side opposite the 30° angle has length 2 and the side opposite the 60° angle has length 2√3 (the length of the longer leg).