Consider the function f(a) = a - 5x on the closed interval [-1, 3]. Find the exact value of the slope of the secant line connecting (-1, f(-1) ) and (3, f(3)). 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=