A wall's height is two-thirds that of its length. The entire wall will be painted. The paint costs $\$ 12$ per gallon, and 1 gallon of paint covers 60 square feet. What expression gives the cost of the paint (assuming one can purchase partial and full gallons) to cover a wall that is $\mathrm{L}$ feet long?
(A) $\quad$ Cost $=L^{2}$
(B) $\quad$ Cost $=\frac{1}{5} L^{2}$
(C) $\quad$ Cost $=\frac{2}{15} L^{2}$
(D) $\quad$ Cost $=\frac{3}{64} L^{2}$