The volume \( V \) of a rectangular pyramid can be calculated using the formula:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
The base area of a rectangular pyramid is given by:
\[ \text{Base Area} = \text{Length} \times \text{Width} \]
For the given dimensions:
- Length = 5 mm
- Width = 8 mm
- Height = 18 mm
First, calculate the base area:
\[ \text{Base Area} = 5 , \text{mm} \times 8 , \text{mm} = 40 , \text{mm}^2 \]
Now, use the base area to find the volume:
\[ V = \frac{1}{3} \times 40 , \text{mm}^2 \times 18 , \text{mm} \]
\[ V = \frac{1}{3} \times 720 , \text{mm}^3 = 240 , \text{mm}^3 \]
Thus, the volume of the rectangular pyramid is
\[ \boxed{240 , \text{mm}^3} \]