A chocolate chip cookie recipe calls for 15 cups of flour for 20 dozen cookies. How many cups of flour are needed for 144 cookies?
Converting 144 to 12 dozen, we see that we are making $\frac{12}{20}=\frac{3}{5}$ as many cookies as the recipe makes.  Therefore, we need $\frac{3}{5}$ as much flour, which is $\frac{3}{5}\cdot15=\boxed{9}$ cups.