The question is essentially asking who's equation works better (Part A) and to explain why (Part B).
Marcella is suggesting the equation 6r + 12 = 683.88
Julia is suggesting the equation 6(r + 12) = 683.88
Six people are on the trip.
It is $12 PER person to rent a floatation device.
The total cost of the trip was $683.88.
Hope I've helped!