Terrell's mom paid $27 for 18 juice boxes for the party. at that rate, how much would she pay for 24 juice boxes?

This is an item involving the use of ratio and proportion. The ratio between the the cost and the number of juice boxes should always be equal. With this,  
                                ($27 / 18 juice boxes) = (x / 24 juice boxes)
Solving x from the equation gives x = 36. Thus, 24 juice boxes cost $36.