Consider the function f(x) = x- 6x on the closed interval [1, 3]. Find the exact value of the slope of the secant line over the interval. m= By the Mean Value Theorem, there exists c in (1, 3) so that m = f'(c). Find all values of such c in (1, 3). Enter exact values. If there is more than one solution, separate them by a comma. C=