Answer:
For more than 180 minutes of phone use.
Step-by-step explanation:
Let m represent number of minutes of phone use in a month.
We have been given that in Plan A, there is no monthly fee, but the customer pays $0.06 per minute of use.
The cost of using m minutes in plan A would be
.
We are also told that in Plan B, the customer pays a monthly fee of $4.80 and then an additional $0.03 per minute of use.
The cost of using m minutes in plan B would be
.
To find the amounts of monthly phone when Plan A will cost more than Plan B, we will set cost of plane A greater than cost of plan B as:

Let us solve for m.




Therefore, Plan A will cost more than Plan B for more than 180 minutes of phone use.