Step-by-step explanation:
since the whole biggest triangle is a right triangle so ,
[tex] {x}^{2} = {20}^{2} + {18}^{2} \\ {x}^{2} = 400 + 324 \\ {x}^{2} = 724 \\ x = \sqrt{724} = 26.907 = 26.91[/tex]
