Front-end estimation is a quick way to estimate a product using the leftmost digits of the numbers. In this case, you can use it to estimate the area of the lawn, which is the product of its dimensions.
Take the leftmost digit of each number:
105 feet becomes 100 feet.
112 feet becomes 100 feet.
Multiply these two rounded numbers:
100 feet * 100 feet = 10,000 square feet.
So, using front-end estimation, the estimated area of the lawn is 10,000 square feet.