Answer:
40.5 centimeters.
Step-by-step explanation:
Given:
The width of the prism is 3 centimeters.
The width of the prism is 1/3 of its length. 
The height of a rectangular prism is half its width.
To find:
<u>Volume of a rectangular prism = ?</u>
Solution:
Width of the prism = 3 cm
As given, height of a rectangular prism is half its width.
height of a rectangular prism = 
Similarly, as given, the width of the prism is 1/3 of its length. 
Width of the prism = 
                             
By multiplying both sides by 3
                             
Thus, length of prism = 9 cm
Now, as we know:

                                                  
Therefore, the volume of a rectangular prism is 40.5 centimeters.