Answer
We can rank the pipes according to their length:
$E \gt A \gt D \gt C \gt B$
Work Step by Step
We can write an expression for the length of pipe A:
$f = \frac{3v}{2L}$
$L = 1.5~\frac{v}{f}$
We can write an expression for the length of pipe B:
$f = \frac{v}{4L}$
$L = 0.25~\frac{v}{f}$
We can write an expression for the length of pipe C:
$f = \frac{3v}{4L}$
$L = 0.75~\frac{v}{f}$
We can write an expression for the length of pipe D:
$f = \frac{5v}{4L}$
$L = 1.25~\frac{v}{f}$
We can write an expression for the length of pipe E:
$f = \frac{7v}{4L}$
$L = 1.75~\frac{v}{f}$
We can rank the pipes according to their length:
$E \gt A \gt D \gt C \gt B$
