For a course trip, (5-10) students have confirmed their participation, and by establishment policy, one representative must attend for each (2-2) students. This tour consists of visiting a water park for the entire day, which costs $(a + 1) per person, an amount that includes transportation, entrance to the park, and food. If the total amount to pay for transportation and tickets for the entire group is $(a - 3)², how much will they pay for food, in terms of a?