Change the unit first

Width 4dm=0.4m, height = 3dm = 0.3m ..

The surface area of each iron sheet is only lateral area, and there is no upper and lower "cover" (that is, the bottom area).

S lateral area of each section = length× height× 2+width× height× 2 = 2 * 0.3 * 2+0.4 * 3 * 2 = 3.6 square meters.

Section 12 cuboid iron outer area 12*3.6=43.2 m2.

So it takes 43.2 square meters to make 12 rectangular tin cigarettes.

I hope I can help you.