Since this is a right triangle, you can use the pythagorean theorem,
, to find XY. Since we know that 15 and 17 are our legs and that XY is the hypotenuse, we can solve it as such:

In short, XY is √514, or 22.67 rounded to the hundreths, units long.
You multiply the 2 together 4 5/6 and 2 2/3.
4 5/6=29/6
2 2/3=8/3
you multiply the tops together then the bottoms together
29*8=232
3*6=18
232/18=116/9