The function f left parenthesis x right parenthesis equals 1.2 x cubed minus 35 x squared plus 270 x plus 552 below models the number of discharges from the military, f left parenthesis x right parenthesis comma of active-duty gay service members under the "don't ask, don't tell" policy x years after 1994. Find the slope of the secant line from x 1 equals 0 to x 2 equals 4.