Life Cycle manufactures and sells exercise bikes. If the price of an exercise bike is $154, then the company sells 213 bikes per week, and the elasticity of demand is -0.462. Assume that the demand function is differentiable and that the only time the company sells exactly 213 bikes per week is when the price of a bike is $154. Given this situation, which of the following do you know MUST be true? [Hint: Recall that marginal revenue is the derivative of revenue with respect to quantity.] a) The marginal profit is positive when Life Cycle sells 213 bikes per week. b) The marginal profit is negative when Life Cycle sells 213 bikes per week. c) The marginal revenue is negative when Life Cycle sells 213 bikes per week. O d) The marginal revenue is positive when Life Cycle sells 213 bikes per week