she has 7 boxes at home, then she goes and buys 6 more from the store, now she has 7 + 6 = 13 boxes of chips, each box of chip has 13 bags, so the total amount of potato chips I guess is 13 * 13 = 169 bags total.
So she split it even among her 9 students, so how many times does 9 go into 169? 169 ÷ 9, has a quotient of 18 with a remainder of 7.
18 * 9 = 162, plus 7 = 169, which is the total amount of potato chips bags.