The ladder is the hypotenuse of a 45 45 90 triangle.
The legs of a 45 45 90 triangle = hypotenuse / sqroot (2)
15 / 1.414 = 10.608
(Incidentally it is the "bottom" of the ladder that is 10.608 feet from the wall. The "top" of the ladder is touching the wall. LOL)
The smallest number subtracted from the problems is 4
Answer:

Step-by-step explanation:
Given


Required
Find y when 
We have:

Express as equation

Solve for k

When 


When
, we have:


