John has a blueprint for a square-shaped office. He decides to change the layout and so draws a new blueprint such that the width of his office increased by 15 feet. The area of his office according to the new blueprint is given by the expression below, where x is the side length, in feet, of the original square-shaped office.

x^2+15x

Which statement best describes the term 15x?

the area of the office according to the old blueprint
the width of the office according to the new blueprint
the area added to the office according to the new blueprint
the area of the office according to the new blueprint