To find the volume of a rectangular pyramid (which is the shape of the cheese wedge), you can use the formula for the volume of a pyramid:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
First, calculate the base area of the rectangular base:
\[ \text{Base Area} = \text{length} \times \text{width} = 9 , \text{cm} \times 4 , \text{cm} = 36 , \text{cm}^2 \]
Next, substitute the base area and the height into the volume formula. The height of the pyramid is given as 21 cm.
\[ V = \frac{1}{3} \times 36 , \text{cm}^2 \times 21 , \text{cm} \]
Now, calculate the volume:
\[ V = \frac{1}{3} \times 36 \times 21 \] \[ V = \frac{1}{3} \times 756 \] \[ V = 252 , \text{cm}^3 \]
Therefore, the volume of the piece of cheese is \( 252 , \text{cm}^3 \).