The numbers 4 and 6 have been rubbed off two squares of this die net (marked ?). The die folded from the net is shown on the right. Which number is on the face opposite 4?

In the net, the two ? squares are opposite 3 and 1 (a square and the one two places along a row are opposite). On the folded die, 4, 6 and 5 meet at one corner in the order top 4 → left 6 → right 5. Only one way of filling the blanks gives that turning order, and it puts 4 next to the 1, i.e. opposite 3. (The other way round would give the mirror-image corner.)