Answer:
A) 10
Explanation:
Given:
Perimeter of rectangular backyard = 200 ft.
Width = 30 ft
Length =
![x+60](https://img.qammunity.org/2020/formulas/mathematics/middle-school/eb8g6ocjt6c4lwyndmlft6owjcjryvod8j.png)
We need to find the value of x.
Now we know that perimeter of rectangle is equal to twice the sum of its length and width.
Framing in equation form we get;
Perimeter of Rectangle =
![2(length+width)](https://img.qammunity.org/2020/formulas/mathematics/high-school/ipwrkw2f5hz2kl3165d6309yoyv4zkzblw.png)
Substituting the given values we get;
![2(x+60+30)=200](https://img.qammunity.org/2020/formulas/mathematics/middle-school/aaj0kjeghu7k7ue2ss82flpme9lgbt0ozb.png)
Using Addition Property we get;
![2(x+90)=200](https://img.qammunity.org/2020/formulas/mathematics/middle-school/herqoj0fhi7uyrtgouwagy37n8i38eukyr.png)
Using Distributive property we get;
![2x+2*90=200\\2x+180=200\\](https://img.qammunity.org/2020/formulas/mathematics/middle-school/xrfq4atf9ljtv8ciifbnryrf8wh8jj8akl.png)
Now Using Subtraction property we will subtract 1800 on both side we get;
![2x+180-180=200-180\\2x=20](https://img.qammunity.org/2020/formulas/mathematics/middle-school/gj87ksqbqp8t51u8225aqcjef9iuaer65o.png)
Now we will use division property and divide both side by 2 we get;
![(2x)/(2)=(20)/(2)\\\\x=10\ ft](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8ef55i6m1als1qxq7ok0p3cdz0w496373y.png)
Hence The value of x is 10 ft.