1. **State the problem:** We need to find the area of a parallelogram with a base of 15 units and a height of 9 units. 2. **Formula for the area of a parallelogram:** $$\text{Area} = \text{base} \times \text{height}$$ 3. **Important rule:** The height must be perpendicular to the base, which is given as 9 units. 4. **Calculate the area:** $$\text{Area} = 15 \times 9 = 135$$ 5. **Answer:** The area of the parallelogram is 135 square units.