Answer:
For a monthly cost of at least $7 and at most $8, you can have between 100 and 110 calling minutes.
Step-by-step explanation:
The problem states that the monthly cost of a celular plan is modeled by the following function:
In which C(x) is the monthly cost and x is the number of calling minutes.
How many calling minutes are needed for a monthly cost of at least $7?
This can be solved by the following inequality:
For a monthly cost of at least $7, you need to have at least 100 calling minutes.
How many calling minutes are needed for a monthly cost of at most 8:
For a monthly cost of at most $8, you need to have at most 110 calling minutes.
For a monthly cost of at least $7 and at most $8, you can have between 100 and 110 calling minutes.