The ladder resting against the house forms a triangle similar to the one in the image below
To answer this question you must use Pythagorean theorem
![a^(2) +b^(2)=c^(2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/awopfne4n7kueo3d70lox1byqwkomjsd2t.png)
a and b are the legs (the sides that form a perpendicular/right angle)
c is the hypotenuse (the side opposite the right angle)
In this case...
a = x
b = 4
c = 20
^^^Plug these numbers into the theorem
![x^(2) +4^(2) =20^(2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/yp5f1suee7rsex1ifh2l92l47iqa5nj0j6.png)
solve for x
+ 16 = 400
= 384
x = 8√6
or
x ≈ 19.5959....
Hope this helped!
~Just a girl in love with Shawn Mendes