Suppose, m be the number of minutes felipw used.
For his phone service, Felipe pays a monthly fee of $20, and he pays an additional $0.04 per minute of use.
Therefore, the total amount paid by him in a month is
![0.04m+20](https://img.qammunity.org/2023/formulas/mathematics/college/5298pbmhjkjyui0mj0736lyslmzj0pnq3a.png)
The least he has been charged in a month is $78.04.
Therefore,
![\begin{gathered} 0.04m+20\ge78.04 \\ 0.04m\ge78.04-20 \\ 0.04m\ge58.04 \\ m\ge1451 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ma0xrnem9aqj4gpal1ljpzbxmowzdr8yzu.png)
So, the possible number of minutes he has used in a month is 1451 minutes or more than 1451 minutes.