A river guide buys protein bars and bottles of water for participants on a rafting trip. Including taxes, the river guide pays $ 2.50 for each protein bar and $ 1.25 for each bottle of water, spending a total of exactly $ 22.50 . Which combinations of protein bars and bottles of water are possible for the given amounts? Select ALL that apply.

Step-by-step explanation:

2.50   for water

1.25     for protein bar   interesting that is exactly half of the water

22.50   exactly was spent

I couldn't come up a slick equation, so I just applied some logic and used brute forced (trail and error) to solve the problem.

2.5Water + 1.25Protein =   22.5  

      8W     +           2P    =   22.5

      6W     +           6P    =   22.5

      4W     +          10P    =   22.5

      2W     +          14P    =   22.5

There are the possible combinations of both protein bars AND water, since he bought both.  He could have also bought 10 water or 18 protein bars, but that is not part of the combination.

i believe the correct answer is b.

its a straight line parallel to the time axis