Q. A friend of yours is considering two cell phones service providers. Provider A charges $120 per month for the service regardless of the number of phone calls made. Provider B doesn't have a rigid service fee but instead charges $1 per minute for calls. Your friend's monthly demand for minutes of calling is given by the equation QD = 150 - 50P, where P is the price of a minute.
A. With each provider. Elucidate the price to your friend of an extra minute on the phone?
B. In light of your answer to (a), how many minutes would your friend talk on the phone with every provider?
C. Explain how much he finishes up paying each provider every month?
D. Explain how much customer extra he obtains with each provider?