Respuesta :

D. 3 √3

I'm using the Pythagorean theorem wherein: a² + b² = c² (hypothenus)

a = unknown
b = 3
c = 6

a² + 3² = 6²
a² = 6² - 3²
a² = 36 - 9
a² = 27
a = √27

a = √9 * 3
a = 3 √3