The answer is A.
We know that p must be larger than d since a discount means something will be cheaper. Then we know that $2.50 is essentially what p-d should equal to (p-d =2.50)
Then you work through the various tables and find which values will consistently give you 2.50 as the difference between p and d.
For example in table A:
3.00-0.15=2.50
4.00-1.50=2.50
5.00-2.50=2.50
6.00-3.50=2.50
