You can
put this solution on YOUR website!
I think you are supposed to see the ladder making a right triangle with the wall and the floor. In math land, all walls are vertical and all floors are horizontal.
|\
| \
H | \ L
= | \
17| \
| \
|======
B = 14
This is a right triangle so the Pythagorean Theorem applies:

which is 22.023 when I round it to the 3rd decimal place.