Large reusable bottles cost $4 more than small ones. eight large bottles cost $24 less than 12 small ones. how much does one small bottle cost?

A small bottle costs $14.

To solve the problem, the equation would be this:

 

Let s represent a small bottle. Since one large bottle is $4 more than a small one, you would write out (4+s). Then, multiply it by 8 to find one side of the equation, and get 8(4+s). To write out the right side of the equation, you would write out 12s to represent 12 small bottles, and subtract 24 from that to represent that 8 large bottles is $24 less than 12 small ones. 

Then, proceed to solve the equation to get the answer of s=14. Because a small bottle is $14, you can check your work by substituting the 14 in replace of s.