It's basically the same as the last one.
Width is 2m.
Length is variable but given once n is chosen
instead of height you are given volume. calculate the height from the volume as before.
height becomes a function of $n$
Then a single strap length is $4+2h$ (I assume there is no strap lengthwise anymore)
You've got $n$ of these so $L=n(4+2h(n))$
Proceed on from there.
$n=2$
$\dfrac 3 2 \leq x < 3$
$V = 2 x h$
$\ell = 2(2\cdot 2 + 2 h) = 8+4 h = 8 + \dfrac{4V}{2x} = 8 + \dfrac{2V}{x}$
$n=3$ is very similar and I'm sure you can figure it out.
I don't know what they mean by optimization. Are you supposed to select a length $x$ for a chosen $n$ such that $\ell$ is minimized?