The answer to the question is 90
The Pythagorean theorem is the idea that the sum of the two legs which are both squared is equal to the hypotenuse's length squared.
*<em>look at the image I attached for a better explanation</em>
By looking at the picture, we are missing the leg's length, and by using the Pythagorean theorem, we get the equation

Thus the <u>missing side length is 12 cm</u>
Hope that helps!
Hey! Good Morning! (if its morning for you) Easy way to figure these things out is to just graph them an take a look. Since we know this is a parallelogram, we can use the basic rules of them to know for sure where that one last point is. (Or we can use the first way, your choice) So just by graphing those points and looking at the incomplete stricter it created,
We can know the last point lies at (0, 2) (I put this spaced so you don't have to read my entire message lol) Hope this helps and good luck!
Figure it out stop being lazy and asking for help