A right angle trangle is used to illustrate the given scenario as shown below
Looking at the diagram,
AC = x represents the length of the ladder
CB = 5 represents the distance of the ladder from the wall
AB = 16 represents the height of the ladder from the ground to the window. We would solve for x by applying the pythagorean theorem which states that
hypotenuse^2 = opposite side^2 + adjacent sde^2
hypotenuse = x
opposite side = 16
adjacent side = 5
Thus,
The length of the ladder must be 16.76 feet