Answer:
D. [tex] 2\sqrt {133}[/tex]
Step-by-step explanation:
[tex] {x}^{2} = {18}^{2} + ( {12}^{2} + {8}^{2} ) \\ \\ {x}^{2} = 324 + (144 + 64) \\ \\ {x}^{2} = 324 + 204 \\ \\ {x}^{2} = 528 \\ \\ x = \sqrt{532} \\ \\ x = \sqrt{4\times 133} \\ \\ x = 2\sqrt {133}[/tex]
