To find the length of line segment \( BC \), we first need to determine the coordinates of points \( B \) and \( C \).
From the question, we have:
- \( B(1, 3) \)
- \( C(9, 3) \)
The points \( B \) and \( C \) both share the same \( y \)-coordinate (which is 3), meaning they lie on a horizontal line.
To find the length of line segment \( BC \), we can calculate the difference between the \( x \)-coordinates of points \( B \) and \( C \):
\[ \text{Length of } BC = |x_C - x_B| = |9 - 1| = 8 \]
Thus, the length of line segment \( BC \) is \( 8 \) cm.
The correct response is: 8 cm.