The volume \( V \) of a rectangular pyramid can be calculated using the formula:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
For a rectangular base, the area \( \text{Base Area} \) can be calculated as:
\[ \text{Base Area} = \text{Length} \times \text{Width} \]
Given the dimensions:
- Length = 8 mm
- Width = 5 mm
- Height = 18 mm
First, calculate the area of the base:
\[ \text{Base Area} = 8 , \text{mm} \times 5 , \text{mm} = 40 , \text{mm}^2 \]
Next, plug the base area and height into the volume formula:
\[ V = \frac{1}{3} \times 40 , \text{mm}^2 \times 18 , \text{mm} \]
Calculating this gives:
\[ V = \frac{1}{3} \times 720 , \text{mm}^3 = 240 , \text{mm}^3 \]
Thus, the volume of the rectangular pyramid is:
\[ \boxed{240} , \text{mm}^3 \]