Desta wants to purchase "The Ultimate Plan" from her cell phone provider. If she enrolls in this plan, she can purchase the latest cell phone from the provider for $250. The plan
consists of unlimited talk and text and 18GB of data for $100 per month. It will cost an
extra $20 per month to add her husband's phone to the plan and an extra $10 per
month to have her tablet connected.
a. Set up Desta's monthly cost function for this plan. Let x represent the number of
months she has been on the plan,
b. What will be her average cost per month be after being on the plan for 3 months?
c. Approximately how many months does Desta have to be in the plan for her average
monthly cost to be $140?