Let the length be x and the width be 4/x.

So the base fee is 4×240=960.

Wall area = 2× (2x+8/x) = 4x+16/x.

So the cost is (4x+16/x) ×160 = 640x+2560/x.

So a ***960+640x+2560/x

Obviously x>0

So 640 x+2560/x >; =2√(640x×2560/x)=2√(640？ ×4)=2560

Take an equal sign when 640x = 2560/x.

x？ =4

x=2

At this time, the minimum value =960+2560=3520.

A: When the length and width are 2 meters, the minimum cost is 3,520 yuan.