A store finds that its sales revenue changes at a rate given by S'(t) = −30t2 + 420t dollars per day where t is the number of days after an advertising campaign ends and 0 ≤ t ≤ 30. (a) Find the total sales for the first week after the campaign ends (t = 0 to t = 7). $ (b) Find the total sales for the second week after the campaign ends (t = 7 to t = 14). $ g