To find the volume of the rectangular prism made up of 4 cubes each measuring 15 inches on each side, we first calculate the volume of one cube.
The volume \( V \) of a cube is given by the formula:
\[ V = \text{side}^3 \]
Substituting in the side length of the cube:
\[ V = 15^3 \]
Calculating \( 15^3 \):
\[ 15 \times 15 = 225 \]
\[ 225 \times 15 = 3375 \]
So the volume of one cube is \( 3375 \) cubic inches. Since there are 4 cubes, we calculate the total volume of the rectangular prism:
\[ \text{Total volume} = 4 \times 3375 = 13500 \text{ cubic inches} \]
Now let's reduce this answer to its simplest fractional form. Since \( 13500 \) is an integer, we can express it as a fraction:
\[ 13500 = \frac{13500}{1} \]
Thus, the answer in a simplified form could be left as is or expressed in terms of a fraction. However, it appears that none of the provided options correspond to the volume we've calculated. Therefore, the answer should be \( 13500 \) cubic inches, but it doesn't match any of the provided responses.
If we missed any detail in the framing of the question or if the units should have been changed, please clarify.