To cover the exterior edges of a rectangular cake measuring 21.9 inches in length and 18.3 inches in width, you need 80.4 inches of fondant.
To calculate the amount of fondant needed to cover the exterior edges of a large rectangular cake with dimensions of 21.9 inches in length and 18.3 inches in width, you must calculate the perimeter of the cake. The perimeter of a rectangle is given by the formula:
P = 2(l + w)
where P is the perimeter, l is the length, and w is the width. Plugging in the cake's dimensions we get:
P = 2(21.9 inches + 18.3 inches) = 2(40.2 inches) = 80.4 inches
Therefore, you would need 80.4 inches of fondant to cover the exterior edges of the cake.