A warehouse contains 3,500 boxes of office supplies. Boxes are added to the warehouse at a rate of 7 boxes per day. Which function can be used to find b, the total number of boxes in the warehouse after d days?

1.b = 3,500d - 7
2.b = 3,500d + 7
3.b = 7d - 3,500
4.b = 7d + 3,500