Final answer:
To calculate the percent decrease in annual cell phone usage, find the difference between the two years and divide it by the previous year's usage.
Step-by-step explanation:
To find the percent of decrease in annual usage, we need to compare the usage from last year to this year and calculate the difference.
The difference between last year's usage and this year's usage is 7,090 - 6,381 = 709 minutes.
Next, we need to calculate the percent decrease using the formula:
Percent Decrease = (Difference / Last year's usage) x 100%
Plugging in the values, we get:
Percent Decrease = (709 / 7,090) x 100% = 9.99%.
Therefore, the percent decrease in annual usage is approximately 9.99%.