Samuel has 28 gallons of saline solution available in two large containers at his pharmacy. one container holds three times as much as the other container. find the capacity of each container.

If we read the question carefully, we soon realize that it's not possible to
answer it with the information it gives us.  It tells us how much solution is
available in the two containers, and that one container CAN hold three times
as much as the other one.  But it never tells us whether or not the solution
available FILLS either of the containers. 

In order to earn any points for this one, I'm going to have to make a big fat
assumption, then use my assumption to re-write the question, and finally
answer the question I wrote.  It hardly seems fair.

Assume:
The 28 available gallons of saline solution completely fill
both containers to their respective brims.

Capacity of one container. . . . . . . 1 time
Capacity of the other container . . . 3 times
Total capacity of both containers . . 4 times

 Since both containers are full to capacity,   

                                       4 times = 28 gallons

Divide each side by  4 :    1 time = 7 gallons

Capacity of one container = 1 time  =            7 gallons
Capacity of the other container = 3 times = 21 gallons

Check:
Both containers together = (7 gallons + 21 gallons)  =  28 gallons    yay!