Grpah of l versus 1/f (sound wave)

[somecelxis]

Homework Statement

to determine the c(end correction ) of sound wave of single end closed tube, the equtaion l +c= (lambda/4 ) is used , i don't understand the gradient is v/4 , then how does the author come up with the speed of sound in air is v=4 ?

Homework Equations

The Attempt at a Solution

 

[haruspex]

how does the author come up with the speed of sound in air is v=4 ?

No, the text means the speed, v, is 4*(gradient of graph).