Answer:
x = 7
Step-by-step explanation:
Before we solve the problem, we can make the following statements:
Area = 21[tex]m^{2}[/tex]
Area = l x w
l = x
w = x - 4
therefore,
(x - 4) x x = 21
[tex]x^{2}[/tex] - 4x = 21
[tex]x^{2}[/tex] - 4x -21 = 0
(x - 7)(x + 3) = 0
x = 7 or x = -3
Since it's impossible to get a positive area with a negative length value, we will reject x = -3.
So, the answer is x = 7
