How to figure out a length of a triangle if only given two lengths?

You cannot

If this is a Right Triangle, you can figure it out with pythagorean theorem

a^2 + b^2 = c^2
a = side
b = side
c = longest side (hypotenuse)
(16)^2 + (30)^2 = c^2
256 + 900 = c^2
1156 = c^2
c = 34

34 is the measure of the length of side Z

And for the future, please make sure your questions are specific so we can help you with them.

You can't.

You can solve a triangle if you know:
* All 3 sides (find angles with Law of Sines)
* 2 sides and an angle (find missing side with Law of Cosines, and other angles with Law of Sines or Law of Cosines)
* 2 angles and a side (though sometimes you may get no solution or 2 solutions) (using Law of Sines)

But you can't solve a triangle if you only know 2 sides and nothing else.

shhrewd assumes that it's a right triangle, which means you'd know that one angle is 90 degrees.  If that's what you meant, then yeah, that can work.  But if you only know 2 sides... you can't solve it.

Pythagoras?

Only if it's a right angle triangle though..

x^2+y^2=C^2

16^2+30^2=c^2

256+900=c^2

sq rt of 1156=c

if it is a right triangle otherwise you will have to use the law of sines to get the correct answer as long as you have an angle or two to plug into the problem.

sorry do not have my calculator to give you the correct answer.