Iam not sure for the awnser but maybe its 3
4d+12
Lets put out the 4 because it can also be pulled out of 12
4(d+3)
Shoutout to @Mdarrow01
Have an amazing day!
For this case we must find the perimeter of the fence, in a circular way, knowing that the perimeter of a circle is given by:

Where "r" represents the radius of the circle, in this case 
Substituting in the perimeter equation we have:

Rationalizing we have:

Taking out common factor
:

Answer:

Option C