To find the length of the line segment \( \overline{RT} \), we can use the information given about the segments \( \overline{RS} \), \( \overline{ST} \), and \( \overline{RT} \).
According to the properties of a line segment, the length of \( \overline{RT} \) is equal to the sum of the lengths of \( \overline{RS} \) and \( \overline{ST} \):
\[ RT = RS + ST \]
Using the given expressions:
- \( RT = 3x \)
- \( RS = 3x - 5 \)
- \( ST = 3x - 1 \)
We can substitute the values of \( RS \) and \( ST \) into the equation:
\[ 3x = (3x - 5) + (3x - 1) \]
Now, simplify the right-hand side:
\[ 3x = 3x - 5 + 3x - 1 \] \[ 3x = 6x - 6 \]
Next, we can isolate \( x \) by moving \( 6x \) to the left side:
\[ 3x - 6x = -6 \] \[ -3x = -6 \]
Dividing both sides by -3 gives us:
\[ x = 2 \]
Now that we have \( x \), we can find the length of \( \overline{RT} \):
\[ RT = 3x \] \[ RT = 3(2) = 6 \]
Therefore, the numerical length of \( \overline{RT} \) is
\[ \boxed{6}. \]