The width of a rectangle measures (5.5d+9.7f)(5.5d+9.7f) centimeters, and its length measures (5.1d-3.5f)(5.1d−3.5f) centimeters. Which expression represents the perimeter, in centimeters, of the rectangle? A. 21.2d+12.4 B. 9.7−7f+21.2d C. 21.2d+12.4f D. 6.2+10.6d