How many linear feet you surround 100 feet of rectangular lawn?

It depends on the shape.

Let's say your lawn is 1 foot by 100 feet, which equals 100 square feet, then the surrounding measurement, called the 'perimeter', is 1+ 1+ 100+ 100 = 202 feet.

Or, if the lawn is, say, 4 feet by 25 feet, which equals 100 square feet, the perimeter is 4+ 4+ 25+ 25 = 58 feet.

If the lawn is perfectly square, its size would be 10 feet by 10 feet, and the perimeter is 10+ 10+ 10+ 10+ = 40 feet.

The same is true for all dimensions in between: the perimeter changes as the shape of the lawn changes.