Question 86752
A visual of the problem can help with these problems
---Step#1: Draw a visual (see below)
{{{ graph( 500, 500,-5, 15, -5, 25, -20/11*x+20) }}}

Imagine the slanted line is the ladder leaning a wall.
Notice it form a right triangle.

For right triangle the length of each side is governed by 
{{{a^2 + b^2 = c^2 }}}
----Step#: Find the lenght of the ladder.
Since your ladder form a right triangle, we can use the equation above.
Let "a" be the "base" of the triangle, which is 11 feet from the wall.
Let "b" be the "height" of the triangle, which is 20 feet from the ground
"c" will be your ladder length.
********Don't foreget to do {{{sqrt(c^2) }}} **************