the net is pretty much the net of a long box, kinda like the one in the example in the picture below. Due to that, we can pretty much assume the two sides sticking up and down, are just two small 6x3 rectangles, namely, they have a height of 3, reason why we assume that, if that if we fold the other sides to make out the box, those two sides sticking out, must be 3m to neatly snugfit.
now, if we close the box as it stands, the sides(laterals) will be on the left-right sides two 3x15 rectangles, and on the front-back sides, two 6x15 rectangles.
we're excluding the top and bottom sides, because those are not "laterals", or sides of the box.
[tex] \bf \stackrel{\textit{two rectangles, left and right}}{2(3\cdot 15)}+\stackrel{\textit{two rectangles, front and back}}{2(6\cdot 15)}
\\\\\\
90+180\implies 270 [/tex]
