Answer
the length of the ladder is
$l=7.84~m\approx7.8~m$
Work Step by Step
We are given the 2 sides of a right triangle.
$a=3.1m$
$b=7.2m$
The length of the ladder (let's call it $l$) can be calculated as the hypotenuse of the right triangle by using the Pythagorean Theorem.
Thus, we have:
$l^{2}=a^{2}+b^{2}$
$l=\sqrt {a^{2}+b^{2}}$
$l=\sqrt {(3.1m)^{2}+(7.2m)^{2}}=7.84~m\approx7.8~m$
