Answer:
The estimate crow is 9777 people
Step-by-step explanation:
A square of 9ft by 9 ft has an area of:

In an area of 81ft, fit 15 people.
Now, lats see the area of one mile by 10ft.
There is 5280 ft in one mile.
Then, the area is:

If we divide the two areas, we get a ratio:

we got 651.85 squares of 81ft^2, and in each one fits 15 people. Thus:

Thus, the estimate is 9777 people in a mile by 10 ft