#### Answer

There are approximately 4,000,000 square feet in 138 acres.
There are exactly 6,011,280 square feet in 138 acres.

#### Work Step by Step

To estimate the square feet in 138 acres use front end rounding to approximate the number of square feet in one acre and to approximate the number of acres.
$43,560 \approx 40,000$
$138 \approx 100$
Then multiply the approximate square feet per acre by the approximate number of acres.
$40,000 \times 100 = 4,000,000$
To find the exact number of square feet in 138 acres, multiply 138 by the number of square feet per acre.
$138 \times 43,560 = 6,011,280$