Answer:
The equation to determine the length is
.
The Length of the exercise mat is 16 feet.
Step-by-step explanation:
Given:
Perimeter of Rectangular mat = 
Let the length of the mat be denoted by 'l'
And width be denoted by 'w'.
Also Given:
The length of the mat is twice the width of the mat.
So we can say that;
⇒ equation 1
Now we know that;
Perimeter of Rectangle is equal to twice the sum of length and width.
framing in equation form we get;
⇒ equation 2
Now Substituting equation 1 in equation 2 we get;

Applying Distributive property we get;

Hence, The equation to determine the length is
.
On Solving the above equation we get;

Dividing both side by 6 we get;

Now Substituting the value of 'w' in equation 1 we get;

Hence The Length of the exercise mat is 16 feet.