The Clearvoice cell phone company is considering investing in additional cell phone towers across the country to improve its coverage and attract more customers. It estimates that if it builds K additional towers, its benefit (the value of its increased future profits) will be B(K) = 500K - K2million dollars, with a marginal benefit of MB(K) = 500 - 2K.Each tower costs 20 million dollars. What is Clearvoice's total cost when it builds Ktowers? What is its marginal cost? Treating its investment as finely divisible, how many cell towers should it build?