Answer: there were 12 red pens in each box
Explanation:
Let x = the number of red pens that were initially in each box.
The college bookstore ordered six boxes of red pens.
This means that the total number of red pens ordered is 6×x = 6x
The store sold 28 red pens last week and 38 red pens this week. This means that the total number of red pens sold = 28 + 38 = 66
The number of red pens left will be the total number of red pens minus the number of red pens that were sold. It becomes 6x - 66
6 pens were left on the shelf. This means that
6x - 66 = 6
6x = 6 + 66 = 72
x = 72/6 = 12