Maria can either buy a basket that contains p pounds of apples for $16

This solution is absolutely true. Just to clarify on statement 1, the reason it's insufficient is that there are up to 20 pounds of apples, so there could be 0, 10, 15, 17 or 19 pounds of apples in the basket. Regardless, the basket costs 16.05$, but the price to get the same amount of apples per pound can be as low as 0$ or as high as 19 x 0.95 = 18.05$.

The only figure to be on the lookout for is when does the amount of apples purchased per pound hit 16.50$, which in this case is between 17 and 18 pounds. ( 16.15$ to 17.10$). If we know for sure which side of this line we lie on, then we have sufficient data. As an example, if the statement had read that the basket contains less than 15 pounds of apples, or if it indicated that the basket contains more than 20 pounds, then the answer would have been D.

Statement 2 as indicated gives a linear equation, so it will give one specific answer (the basket has 15 pounds of apples in it), and is therefore sufficient without requiring any math calculations.

Hope this helps!
-Ron