Answer:
Equation: [tex]20=4x[/tex] or [tex]x=\frac{20}{4}[/tex]
Solution: [tex]x=5[/tex]
Step-by-step explanation:
The formula that is used to calculate the perimeter of  a square is:
[tex]P=4s[/tex]
Where "s" is the side lenght the square.
Knowing that Xin used  20 yards of fencing to build the walls of a square chicken coop (in which the lenght in yards of each wall is represented with "x"), you can identify that:
[tex]P=20\\\\s=x[/tex]
Then, you can susbtitute values into the formula [tex]P=4s[/tex]:
[tex]20=4x[/tex]
Finally, you must solve for "x" in order to find its value.
This is:
[tex]\frac{20}{4}=x\\\\x=5[/tex]
