Answer:
Basicallly, if the machine packs 2/3 of a box every 1/2 min, then the machine will pack twice as many boxes for 1 min, since 1/2 multiplied with 2 is 1.
2/3 multiplied with 2 is 4/3.
Therefore, the machine can pack 4/3 boxes per minute.
(what my research says)