Use the Pythagprean theorem:

We have:

Substitute:
Yes that is the answer 19
Let's use the SAS postulate! SAS means Side, Angle, Side. I would sometimes write this the other way and get in trouble, haha.
It technically means if a triangle that has a congruent angle between two congruent sides, it means it is congruent. Here is a picture.
Answer:
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Step-by-step explanation: