Doubling the width would use less cardboard.
Justification:
Doubling the height will use 9in more cardboard
Doubling the width will only use 2 more inches of cardboard
204/68=3, 207/69=3, 210/10=3, 213/71=3, 216/72=3, 219/73=3
Yes, by the time you add up all estimations, you must add taxes.