Answer: If the barn is at least 60 feet long, the farmer can make the pen 60 by 30. That will result in an area of 1800 square feet.
Step-by-step explanation: You can try any combinations of dimensions that add up to 2w + 1L = 120
For example:
2(20) + 80 = 120 Area = 20 × 80 = 1600 square feet
2(25) + 70 = 120 Area = 25 × 50 = 1750 square feet increasing
2(30) + 60 = 120 Area = 80 × 40 = 1800 square feet = MAX
2(35) + 50 = 120 Area = 35 × 50 = 1750 sq ft decreasing again
