Answer:
$103.10.
Step by step explanation:
Let's assume that Carlos uses "m" minutes in a month.
The additional fee he pays based on the number of minutes he uses would be 0.06 * m.
Therefore, his total cost in a month would be the sum of the monthly fee and the additional fee:
Total cost = Monthly fee + Additional fee
Total cost = $20 + $0.06 * m
We know that the least he has been charged in a month is $103.10.
Therefore, we can set up an inequality:
$103.10 ≤ $20 + $0.06 * m
Solving for "m":
$103.10 - $20 ≤ $0.06 * m
$83.10 ≤ $0.06 * m
m ≥ $83.10 / $0.06
m ≥ 1385
Therefore, Carlos must have used at least 1385 minutes in a month to be charged a minimum of $103.10.