A rectangle is a four sided shape with 4 perpendicular angles. It has two pairs of parallel sides which are equal in distance: width and length. Its area, the amount of space inside it, can be found using the formula A = l*w. If the area is 600.6 m² and the length is 7.8m, you can solve for the width by dividing the area by the length. Division is the inverse operation of multiplication and it will isolate the width.
600.6 / 7.8 = 77 inches.
On contrast, the perimeter is the distance around the shape. It si found by adding all sides together in the formula P = 2l + 2w. Substitute l = 7.8 and w =77.