To find the volume \( V \) of a right rectangular prism, you use the formula:
\[ V = \text{Base Area} \times \text{Height} \]
Given that the base area \( B = 21 , \text{cm}^2 \) and the height \( h = 3 , \text{cm} \), we can substitute these values into the formula:
\[ V = 21 , \text{cm}^2 \times 3 , \text{cm} = 63 , \text{cm}^3 \]
Thus, the volume of the right rectangular prism is \( 63 , \text{cm}^3 \).
So the correct response is:
63 cm³