Question 838146
distance from wall to the foot of ladder be x
The distance from top of ladder to the ground=(x+4)
Ladder length = 20 feet

The ground wall and ladder form a right triangle

apply Pythagoras theorem

x^2+(x+4)^2=20^2

x^2+x^2+8x+16=400

2x^2+8x-400+16=0
2x^2+8x-384=0
/2
x^2+4x-192=0
complete the squares

x^2+4x+4-4-192=0

(x+2)^2= 196

take the positive square root

x+2=13
x=11

(x+2)=13

distance from wall to the foot of ladder 11 feet
The distance from top of ladder to the ground=13 feet