Help with secondary 1 science/math equation problem

[Cluel]

i am homeschooled and it’d be really helpful if someone can explain the solution for (d): (i) and (ii)
ignore my answer for (a) i know that i should multiply by 2

 

[Cluel]

oops there’s only one wavelength

 

[HOI]

The distance from A to B is 12 m and you are told that this is $1\frac{1}{2}= \frac{3}{2}$ wavelength.
So one wave length is $\frac{1}{\frac{3}{2}}= \frac{2}{3}$ of 12 m= 8 m.

 

[skeeter]

part (d) states that it takes 37.5 seconds to transfer energy from A to B, a distance of $1.5 \lambda$

wave speed is $v = \dfrac{12\, m}{37.5 \, sec} = \dfrac{8 \, m}{t \, sec}$ ... solve for $t$

finally, $f = \dfrac{v}{\lambda}$

 

[Cluel]

part (d) states that it takes 37.5 seconds to transfer energy from A to B, a distance of $1.5 \lambda$

wave speed is $v = \dfrac{12\, m}{37.5 \, sec} = \dfrac{8 \, m}{t \, sec}$ ... solve for $t$

finally, $f = \dfrac{v}{\lambda}$

37.5 / 12 x 8 = 2.5s?
or 12 / 37.5 = 0.32
8 / 0.32 = 25s

 

[skeeter]

$t = \dfrac{37.5 \cdot 8}{12} = 25 \, sec$

or, thinking proportionally, the wave travels three half wavelengths in 37.5 sec ... it would travel two half wavelengths (1 whole $\lambda$) in 2/3 the time.