9 ft is the answer because a square has four sides, so 36 divided by 4 is 9
        
             
        
        
        
(4 feet wide), 12 feet in length. 4*3=12    4*12=48
        
             
        
        
        
Answer:
The solution is x = -2, y = -3
Step-by-step explanation:
Let's start with the equation 3x + y = -9
Substitute the y for 5x+7 seen in the second equation
Now you have 3x + (5x+7) = -9
Lets solve:
Let's add the x's
Now we have 8x + 7 = -9
Substracy seven from each side
Now we have 8x = -16
Now let's divide 8 on each side
Now we have x = -2
Now lets plug in -2 to the second equation
The second equation is y = 5x+7
When we plug in -2 we get y=5(-2)+7
We multiply 
We now have y = -10+7
Add
y = -3
The solution is x = -2, y = -3