A cuboid has six faces, and the upper and lower faces are equal. Left and right faces, etc. The front and back are also equal.

The expanded diagram of the cube is easier to see. Let me talk about the identification method of a cuboid expansion diagram. Of course, the best way is to unfold a cuboid, first find the bottom and fix it on the top. Let the back find the front, then the side equal to it is the back; Then the rest is left and right.

Ribbon for packaging gift boxes: Ribbon crosses on both sides, so the length of ribbon should be equal to 2 long and 2 wide first; There should be ribbons from bottom to top, front, back, left and right, so the length of ribbons is equivalent to four heights. Then, the total length of the ribbon is two lengths+two widths+four heights+the length of the ribbon at the knot.

2× (15+10)+8× 4+18 =100 (cm)