Net−4−$-4-$You is an Internet Service Provider that charges its 1$1$ million customers $19.95$19\mathrm{.}95$ per month for its service. The company's variable costs are $.50$\mathrm{.}50$ per customer per month. In addition, the company spends $.50$\mathrm{.}50$ per month per customer, or $6$6$ million annually, on a customer loyalty program designed to retain customers. As a result, the company's monthly customer retention rate was 78.8$78\mathrm{.}8$ percent. Net−4−$-4-$You has a monthly discount rate of 1$1$ percent.

a.$.$ What is the customer lifetime value?

b.$.$Suppose the company wanted to increase its customers' monthly retention rate and decided to spend an additional $.20$\mathrm{.}20$ per month per customer to upgrade its loyalty program benefits. By how much must Net 4−$4-$You increase its monthly customer retention rate so as not to reduce customer lifetime value resulting from a lower customer margin?

Answers

a)85.36$)85\mathrm{.}36$$

b)1.5($)1\mathrm{.}5($Decrease from 78.8$78\mathrm{.}8$ to 77.03)$77\mathrm{.}03)$

For a the formula used to get the answer is

18.95(1/1+0.01−0.788)=85.36$18\mathrm{.}95(1/1+0\mathrm{.}01-0\mathrm{.}788)=85\mathrm{.}36$

How do I get the right answer for b?$?$