You use the Pythagorean Theorem.
A squared + B squared = C squared
The length of the ladder (which is 10) would be the hypotenuse (c) and the distance it is away from the bottom of the tree (4 feet) can be your a or b.
so you would do 4 squared + b squared= 10 squared
16+b squared=100
b squared = 84 (100-16). Now at the end, you square root your answer so now it would be b= 9.1651513 or just rounded to 9.17
