The person should order around 10,941 pens to get through 3 weeks of school.
Sales are actions involving the sale of goods or the volume of items sold during a specified time frame. A sale also includes the provision of a service for a fee.
Here, 521 pens are sold per day in the school store.
The number of days present in 3 weeks is 21 days.
Then, for 21 days, the number of pens required is calculated by multiplying the number of days and the number of pens.
So, 21 x 521 = 10,941 pens.
Therefore, the person should order 10,941 pens.
To know more about sales:
https://brainly.com/question/28618654
#SPJ4