If it looks like this:
A -------------------- B
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C -------------------- D
Then BC is the hypotenuse of a right triangle with sides 16 and 30. Using the Pythagorean Theorem you can solve for the length of the hypotenuse:
\(h^2 = 16^2 + 30^\)
\(h= \sqrt{256+900}\)
\(h =34\)
