Answer:
23, 24, 25
Step-by-step explanation:
Weight of 5 lb boxes = 5x
Weight of 10 lb boxes = 10y
Total weight should be greater than 30 lbs.
5x + 10y > 30
The third option is correct.
The subspace has dimension 3.
Intuitively, you can think that you're removing one degree of freedom from
. In fact, this space is generated by the following span:

Since the first and third coordinate must be the same, we have
. So, the span becomes

which is the same as

And so you can see that the space is generated by three vectors.