A city has been growing rapidly in recent decades, especially with regard to constructing large buildings. A city planner noticed that the number of large buildings in the city after 3 years can be modeled by the equation B = 30 x 3" . In this equation, what does 3* represent? A The number of buildings increases by a factor of x each year for 3 years B The number of buildings increases by x buildings every year The number of buildings increases by a factor of 3 every year D The number of buildings increases by 3 buildings each year