The formula for the volume of a rectangular pyramid is given by:
\[ V = \frac{1}{3} \times \text{base area} \times \text{height} \]
Given that the length is 7 cm and the width is 9 cm, the base area of the pyramid can be calculated as:
\[ \text{base area} = 7 \times 9 = 63 \, \text{cm}^2 \]
Plugging in the values for the volume and base area into the formula, we have:
\[ 231 = \frac{1}{3} \times 63 \times \text{height} \]
Solving for the height:
\[ \text{height} = \frac{231}{\frac{1}{3} \times 63} \]
\[ \text{height} = \frac{231}{21} \]
\[ \text{height} = 11 \, \text{cm} \]
Therefore, the height of the rectangular pyramid is 11 cm.