Find the perimeter of a rectangle if one-eighth of its area is 12 cm2 and its length is 12 cm.

We have to find what the area of the rectangle is. Since it is known that 1/8 of its area is 12 cm2, we must divide 12 cm2 by 1/8.

12 / 1/8 = (12/1) / (1/8) = (12/1) * (8/1) = (12 * 8) / 1 = 96/1 = 96 (cm2).

Now we can calculate what is the second side of the rectangle using the formula S = a * b, where S is the area, a and b are the width and length of the rectangle.

96 = 12 * b, b = 96/12 = 8 (cm).

The perimeter of the rectangle is P = 2 (a + b) = 2 * (12 + 8) = 2 * 20 = 40 cm.

Answer: 40 cm.