Jeff S. answered 05/21/20
Learn by Doing and Understanding
Hi Joey.
We don't know the angle from your post, but assume the angle is θ. You can then use the Law of Cosines.
Here's a hint for memorizing the law: It starts with the Pythagorean Theorem (which you've surely memorized): c2 = a2 + b2. This is used to find the length of side c, which is the hypotenuse of the right triangle.
To find the third side, called c, of a non-right triangle is almost the same. If we are given the angle θ which is opposite side c, then we have
c2 = a2 + b2 - 2ab cosine(θ).
Substitute your values and off you go.