In all 30-60-90 triangles, the side lengths are in the ratio , where is the side opposite to the 30 degree angle and is the hypotenuse of the triangle. Since the side opposite to the 30 degree angle is marked as 3, the value of must be .
Alternatively, we can use basic trig. for a right triangle to solve. In any right triangle, the tangent of an angle is equal to its opposite side divided by its adjacent side. Thus, we have: