Answer :

To find this, use the Pythagorean theorem; [tex] a^{2} + b^{2} = c^{2} [/tex]
x=√55mm, and y=3mm
(√55)²+3²=z²
55+9=z²
64=z²
√64=z
8=z
z=8mm
The answer is C: 8mm