A triangle with 30°, 60° & 90° angles is called a semi equilateral triangle.
In such a triangle the hypotenuse equal the side of the equilateral triangle, and the opposite side to the angle 30° is equal half the side of the equilateral or half the hypotenuse.
Assume the side equal 8 & the other 8/2 = 4. let's calculate the 3rd side by applying Pythagoras:
8² = 4² + x² ; 64 = 16 + x² or x² = 64-16 ; x² =48 and x =√48 = √16. 3 = 4√3
If we say that side "a" is the shortest (adjacent), side "b" is the second shortest (opposite), and side "c" is the longest (hypotenuse): then angle A would be 30°, angle B would be 60°, and angle C would be 90°
tan B = b/a or a tan B = b
they have 4 as the smallest value in all four options, so we know that a=4
4 tan 60° = b tan 60° = √3 so, 4 tan 60° = 4√3 b=4√3