To find the length of the diagonal of a cube, we can use the formula:
\[ d = a \sqrt{3} \]
Where \( d \) is the length of the cube's diagonal and \( a \) is the length of an edge of the cube.
In this case, the length of the edge \( a = 8 \) inches. We can plug this value into the formula:
\[ d = 8 \sqrt{3} \]
Now, calculating \( \sqrt{3} \):
\[ \sqrt{3} \approx 1.732 \]
Now substituting this value back into the equation:
\[ d \approx 8 \times 1.732 \approx 13.856 \]
Rounding this to the nearest tenth gives:
\[ d \approx 13.9 \text{ in} \]
Thus, the length of the diagonal of the cube is approximately 13.9 in.