Answer
12.8 ft
Work Step by Step
Use the Pythagorean Theorem. Let l be the length of the ladder.
$l^2=8^2+10^2$
Simplify.
$l^2=64+100$
$l^2=164$
Take the square root of each side.
$\sqrt{l^2}=\sqrt{164}$
Simplify and round.
$l\approx12.8$