30) The function for a current is I(t) = 9 cos(120t) where / is the current, in amperes, and t is the time in seconds. a) Find the current when t = 6 s. b) The electromotive force, E(t), in a circuit, is given in volts by finding the first derivative of the current function /(t). Find the function for the electromotive force E(t). c) Determine the electromotive force when t = 3. d) Find the maximum and minimum electromotive forces and the times that they occur.