A community recreation center has collected a total of 618 donated tickets for free ice cream. Beginning on the second day of summer vacation, the recreation center randomly selects 7 children to each receive one of the free ice cream tickets. Assuming the recreation center continues this pattern of giving away tickets to 7 children each day, which explicit formula shows the number of ice cream tickets remaining at the end of the day, after n number of days?

an=618−7n

an=7n−618

an=618−7(n−1)

an=7(n−1)−618