Top question on the first page.
Ans: Dice net D
Explanation:
Since the opposite sides needs to sum to 7, the net requires the opposite faces to add up to 7.
In net D, notice the side with 4 dots. You need the opposite side of 4, so you go up by two and the side opposite to 4 is 3 dots.
4 + 3 = 7
The same thing goes for side 2. Go up by two faces and you see the 5 dots side.
2 + 5 = 7
1 dot side and 6 dot side add up to 7.
This net is proven to have opposite sides to sum up to 7.
Top question on the second page.
Ans: 18 edges
The original edges of a cube is 12 but since he cut two corners, it generated 3 edges per cut.
So,
12 + 2(3)
12 + 6
= 18
