Answer:

1.    y = 2x + 4 is an equation that matches this problem.

              3

2.   In this situation the y-intercept is (0, 4).  If this is a cost then one interpretation would be that the cost for no items would mean there were other expenses not associated with the item described with the x value.  This could be fixed cost such as insurance, sitting fee for photographs, set-up fee for a cell phone, or rent.