Step 1 :\( h = 6 \text{ feet} \)
Step 2 :\( H = 20 \text{ feet} \)
Step 3 :\( \frac{dd}{dt} = -5 \text{ feet/second} \)
Step 4 :\( \frac{h}{l} = \frac{H}{d + l} \)
Step 5 :\( hd + hl = Hl \)
Step 6 :\( hd = l(H - h) \)
Step 7 :\( l = \frac{hd}{H - h} \)
Step 8 :\( \frac{dl}{dt} = \frac{h}{H - h} \frac{dd}{dt} \)
Step 9 :\( \frac{dl}{dt} = \frac{6}{20 - 6} (-5) \)
Step 10 :\( \frac{dl}{dt} = -\frac{30}{14} \)
Step 11 :\( \boxed{\frac{dl}{dt} = -\frac{15}{7}} \)