To find the volume of a triangular pyramid (also known as a tetrahedron), we can use the following formula:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
Given:
- Height \( h = 7.5 \) inches
- Base Area \( A = 12 \) square inches
Now, substitute the values into the volume formula:
\[ V = \frac{1}{3} \times 12 \times 7.5 \]
Now calculate the multiplication:
\[ 12 \times 7.5 = 90 \]
Now substitute back into the volume formula:
\[ V = \frac{1}{3} \times 90 \]
Calculate the final volume:
\[ V = 30 \]
Thus, the volume of the stereo system is
\[ \boxed{30} \text{ cubic inches}. \]