Each friend gets an equal share. So <em><u>out of the 24 bottles, everyone gets 6</u></em>, or 25% of one case.
<em><u>Each bottle costs $1.25</u></em>. We're being asked to <u>make this equation in terms of cases, though, so this price needs to be multiplied by 6</u>, since we want to know what the individual friends will need to pay. <u>The cost will then be $7.50.</u>
<u>Since this is the price they need to pay per case, we can make our equation:</u>
f(c) = 7.50c is your answer.