Problem
A straight strip of four wraps right around the cube, so the 1st face meets the 3rd and the 2nd meets the 4th.
Wrapping a 4-square strip around a box is like wrapping a paper band around a tin can: square 1 ends up facing square 3, and square 2 faces square 4.
6.G.A.4Create A Physical RepresentationIn a straight strip of four squares, the first and third faces end up opposite each other, and so do the second and fourth.
Folding a straight strip of four wraps it all the way around the cube and brings the fourth square back against the first, closing a band.
Going round that band, a face and the one two steps along it are the pair that face each other across the cube.
The band closes after four faces, so stepping two along from any face lands on the one directly across from it.
Opposite faces add to 7, so A = 7 - 1 = 6 and B = 7 - 2 = 5.
Once you know which faces sit back-to-back, you just subtract from 7 to fill each blank.
6.G.A.4Visualize Spatial RelationshipsThe two flaps outside the strip become top and bottom, so C = 7 - 3 = 4.
After the band of four uses up two opposite pairs, the only faces left are the top and bottom flaps, so they must be opposite each other.
6.G.A.4Draw A DiagramNow compare the three numbers: A = 6, B = 5, C = 4. The smallest is 4, which is on face C.
With all three filled in, picking the smallest is just reading off the lowest number.
6.G.A.4Visualize Spatial RelationshipsFold the net in your mind to see which faces end up back-to-back, then use 'opposite faces add to 7' to fill in every blank.