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 pyramid, the base area is given by the width \( w \) and length \( l \):
\[ \text{Base Area} = w \times l \]
In this case, the width is 4 cm, the length is 3 cm, and the height is 12 cm.
First, calculate the base area:
\[ \text{Base Area} = 4 , \text{cm} \times 3 , \text{cm} = 12 , \text{cm}^2 \]
Now, use the volume formula:
\[ V = \frac{1}{3} \times 12 , \text{cm}^2 \times 12 , \text{cm} \]
Calculating the volume:
\[ V = \frac{1}{3} \times 144 , \text{cm}^3 = 48 , \text{cm}^3 \]
Thus, the volume of the rectangular pyramid is
\[ \boxed{48 , \text{cm}^3} \]