.
The question is closely related to this problem:
How many subsets does the set of 4 elements have ?
The answer is = 16, including empty subset and the improper subset.
So, you can place one subset to one of the two boxes and the rest to the other box.
But the empty subset and the improper subset are excluded by the condition, so only 16-2 = 14 opportunities are available.
Answer. 14.
This way solving the problem becomes especially useful / (effective) when the original set has MANY elements,
so that the direct listing of subsets becomes unpractical.