Hello!
Since this triangle is what I like to call a "45er", and both legs of a 45er are equal, we can now apply the Pythagorean Theorem to find the measure of the hypotenuse.
![12^2 + 12^2 = c^2 144 + 144 = 288 √(288) = 16.9](https://img.qammunity.org/2019/formulas/mathematics/middle-school/zb2eltyuqpvmn2krkfv6gpzbrh6sv6f3fw.png)
(Rounded)
Your answer is 16.9. Round this to 17 if the question is looking for a whole number. :)