Sprint is curious as to how much value each customer provides to the firm. Management has

estimated that it currently costs $$5$ on average to acquire and attract a new customer. Most

customers sign up for the $$\frac{79\mathrm{.}99}{?}$ month phone plan with a margin of $$61\mathrm{.}99.$ Past audits of the

firm's data suggests that most customers remain with Sprint for $7$ years.