6. Jack and Jenny start hiking from the trailhead up to the fire tower on the mountain. Jenny is carrying a heavy backpack and walking slowly. Jack starts at a speed of 4 miles per hour, and when he reaches the halfway point, the trail becomes steeper, reducing his speed to 2 miles per hour. Upon reaching the fire tower, Jack immediately turns back and descends the steep trail at a speed of 3 miles per hour, meeting Jenny at the halfway point. What is Jenny's average speed before they meet? ( )
(A) $\frac{12}{13}$
(B) 1
(C) $\frac{13}{12}$
(D) $\frac{24}{13}$
(E) 2
6. A.

Let the journey from the path at the foot of the mountain to the fire tower at the top be $S$. Then
$$
\bar{V}=\frac{\frac{1}{2} S}{\frac{1}{\frac{2}{4} S}+\frac{1}{\frac{2}{2}} S+\frac{\frac{1}{2} S}{3}}=\frac{1}{\frac{1}{4}+\frac{1}{2}+\frac{1}{3}}=\frac{12}{13} .
$$