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?