ANSWER
The equations that apply are: B and D
Step-by-step explanation
The blanket with the border is:
The area of the border is the total area of the blue rectangle minus the area of the black rectangle - which is the blanket.
The width of the blue rectangle is: 3 + 2x - because we have a border with x width on both sides.
The length of the blue rectangle is: 4 + 2x.
The area of the blue rectangle is:

This area minus the area of the black rectangle - which is 3(4) must be 6 square feet - the area of the border:

If we take the area of the black rectangle to the other side of the equality:
