The formula of a rectangular prism is l<em> </em>x <em>w </em>x <em>h</em> where b represents the length, w represents the width and h represents the height. In this case, you can replace each of these variables with the values given in your problem so it should appear as 2 x 2.25 x 4. Multiply all of these values, and you should get the volume.
Therefore, the volume of the prism is 18 inches cubed.