A storage facility has two sizes of rental units. If square boxes are stored on the bottom of the smaller unit, the unit can hold 7 box lengths along its length and 6 box lengths along its width. The larger unit can hold 6x more box lengths along the length, and 3x more box lengths along the width. Which of the following functions will give the total number of boxes that can fit along the bottom of the larger storage unit? A. L(x) = 18x^2
B. L(x) = 18x^2 + 60x + 42
C. L(x) = 18x^2 + 42
D. L(x) = 18x^2 + 57x + 42