For his phone service, Michael pays a monthly fee of $16, and he pays an additional $0.04 per minute if use. The least he has been charged in a month is $69.52.

Answer: The least number of minutes that he has used his phone in a month is 1248

Step-by-step explanation:

Let m represent the number of minutes that he used his phone in a month.

For his phone service, Michael pays a monthly fee of $16, and he pays an additional $0.04 per minute if use. This means that if he used m minutes in a month, the total cost would be

16 + 0.04m

The least he has been charged in a month is $69.52. This means that

16 + 0.04m ≥ 65.92

0.04m ≥ 65.92 - 16

0.04m ≥ 49.92

m ≥ 49.92/0.04

m ≥ 1248 minutes