To find the total length of \( BD \), we can use the information given about the segments \( AE \) and \( ED \).
We know:
- \( AE = 3x \)
- \( ED = -4x + 21 \)
Since \( E \) lies on segment \( BD \), we can express the total length \( BD \) as the sum of \( AE \) and \( ED \):
\[ BD = AE + ED = 3x + (-4x + 21) \]
Simplifying this expression, we have:
\[ BD = 3x - 4x + 21 = -x + 21 \]
Next, we need to determine the value of \( x \). However, we are not provided any additional information that specifically gives us the value of \( x \). Therefore, we can examine the possible options for the total length of \( BD \):
- Let’s evaluate the given responses:
-
If we let \( -x + 21 = 18 \):
- \( -x = 18 - 21 \)
- \( -x = -3 \)
- \( x = 3 \)
-
If we let \( -x + 21 = 27 \):
- \( -x = 27 - 21 \)
- \( -x = 6 \)
- \( x = -6 \) (not valid since \( x \) must be positive in a length context)
-
If we let \( -x + 21 = 3 \):
- \( -x = 3 - 21 \)
- \( -x = -18 \)
- \( x = 18 \)
-
If we let \( -x + 21 = 9 \):
- \( -x = 9 - 21 \)
- \( -x = -12 \)
- \( x = 12 \)
-
The only sensible findings for \( x \) lead us to \( x = 3 \), which corresponds to the \( BD \) total being:
\[ BD = -3 + 21 = 18 \]
Thus, the total length of \( BD \) is:
\[ \boxed{18} \]