So this is a special triangle. The 30-60-90 triangle rule states that if the short leg is y, then the hypotenuse is 2y and the long leg is y√3.
In this case, the short leg is 5√3 since that times √3 makes 15.
Now with the hypotenuse, just multiply 5√3 with 2, and your answer should be 10√3, or C.
