Xiao Ming bought three cuboid gift boxes of the same size. They are 20cm in length, 15cm in width and 4cm in height. They should be packed into a big box with wrapping paper There are several packaging schemes? How many square centimeters of paper are needed for each scheme? Which kind of packaging is the most economical? (joints and overlaps are ignored)

Xiao Ming bought three cuboid gift boxes of the same size. They are 20cm in length, 15cm in width and 4cm in height. They should be packed into a big box with wrapping paper There are several packaging schemes? How many square centimeters of paper are needed for each scheme? Which kind of packaging is the most economical? (joints and overlaps are ignored)

In the first way, the cuboid is placed in a row horizontally. The length of the cuboid is 20 * 3 = 60 cm, the width and height remain unchanged, and the surface area is (60 * 15 + 60 * 4 + 15 * 4) * 2 = 2400 square cm
In the second way, the cuboid is placed in a row. The length of the cuboid is unchanged, the width is changed to 15 * 3 = 45 cm, the height is unchanged, and the surface area is (20 * 45 + 20 * 4 + 45 * 4) * 2 = 2320 square cm
In the third way, the cuboids are stacked up and down in a row. The length and width of the cuboids remain unchanged. The height becomes 4 * 3 = 12 cm, and the surface area is (20 * 15 + 20 * 12 + 15 * 12) * 2 = 1440 square cm
The third way is stacking up and down, which is the most economical way

A kind of rectangular shaped moon cake box, 30cm long, 15cm wide and 4cm high. Mother bought two boxes and wrapped them with wrapping paper to give them to grandma. At least how much wrapping paper should be used

(30*15+30*4+15*4)*2*2-30*15*2
=(450+120+60)*4-900
=630*4-900
=2520-900
=1620 square centimeters

A biscuit is 30cm in length, 15cm in width and 20cm in height. Now we need to stick wrapping paper on it. What's the area of the wrapping paper?

（30x15+15x20+30x20）x2