This is a special right triangle called a 30-60-90 triangle. It has a special property the relates the ratio of side lengths. That ratio is 1::2
What does this mean? If you know the shortest side of a 30-60-90 triangle, you can find the longer leg by multiplying it by , and you can find the hypotenuse by multiplying the short leg by 2.
In the picture, note that the short leg of the triangle has a length of 9. Therefore, the long leg(or n) is simply 9