I'll leave the picture to you; draw a rectangle and write 2x+4 along the length and 4x along the width. We don't really know the aspect ratio of the rectangle until we know x so any rectangle is fine.
The perimeter is the sum of all four side lengths,
p = (2x + 4) + 4x + (2x + 4) + 4x
Answer: p = 12x + 8
