The angle between the legs of length 16 and 18 has measure 90 + 55 = 145 degrees.
Now use the law of cosines: it says [tex]d[/tex] satisfies
[tex]d^2=16^2+18^2-2(16)(18)\cos145^\circ[/tex]
and solving for [tex]d[/tex] gives
[tex]d=\sqrt{16^2+18^2-2(16)(18)\cos14^\circ}\implies d\approx32[/tex]
so the answer is C.