perimeter of rectangle is calculated by taking the sum of all the sides of the rectangle. In rectangles the 2 opposite sides are equal
length - 3x - 1
breadth - 3x - 3
the formula used to calculate perimeter for rectangle
perimeter = (2 x length) + (2 x breadth)
substituting length and breadth
perimeter = {2 x (3x - 1)} + {2 x (3x - 3)}
= 6x - 2 + 6x - 6
= 12x - 8
therefore correct answer is
b.12x-8