To find the volume of a right rectangular prism (box), we use the formula:
\[ \text{Volume} = \text{Base Area} \times \text{Height} \]
In this case, the base area (B) is given as \(21 , \text{cm}^2\) and the height (h) is given as \(3 , \text{cm}\).
Now we can substitute the values into the formula:
\[ \text{Volume} = 21 , \text{cm}^2 \times 3 , \text{cm} = 63 , \text{cm}^3 \]
Thus, the volume of the right rectangular prism is \(63 , \text{cm}^3\).
The correct response is:
63 cm³.