The answer is [tex]\frac{17}{\sqrt{253}}[/tex] which is the fraction of 17 over sqrt(253). The notation "sqrt" is shorthand for "square root"
Check out the attached image to see the steps on how I got that answer.
Edit: if you need the steps for the pythagorean theorem, then....
a^2+b^2 = c^2
6^2+b^2 = 17^2
36+b^2 = 289
b^2 = 289-36
b^2 = 253
b = sqrt(253)
So that's how I got the square root of 253 as the adjacent side