The mechanical advantage (MA) of an inclined plane can be calculated using the formula:
\[ \text{Mechanical Advantage (MA)} = \frac{\text{Length of the Inclined Plane}}{\text{Height of the Inclined Plane}} \]
In this case, the length of the inclined plane is 9 feet, and the height is 3 feet. Plugging these values into the formula gives:
\[ \text{MA} = \frac{9 \text{ feet}}{3 \text{ feet}} = 3 \]
Thus, the mechanical advantage of the inclined plane is 3.