55. Student Loans Interest rates for subsidized Stafford loans can be approximated for the years 2007 to 2014 by the function f(x) = .15.x2 3.6x + 25, where x = 7 corresponds to the year 2007. According to this model, during what year were interest rates lowest, and what was the lowest interest rate? (Data from: www.studentaid.ed.gov.)