Easiest way to do this is to focus of 'using up' the perimeter.

Now in this case, I had just started with 25x25=625, which showed me that there was certainly no problem making 600 or more square feet out of 100ft perimeter.

Then I just looked at the fact that they're both nice round numbers and thought 'Hmm... Factor 6=1, 2, 3, 6...reciprocal numbers look good, so decided on a 20ft wide square, and checked remainder (20 for one side + 20 for the other = 40, 40 from 100 = 60, 60 divided by 2 <for each side> = 30ft), giving me a 30ft opposite side, then do the math (it's pretty quick) 20x30= (2x3=6 + 100) is 600 sqr ft.

Hope that helps, and you have a great day!

Now in this case, I had just started with 25x25=625, which showed me that there was certainly no problem making 600 or more square feet out of 100ft perimeter.

Then I just looked at the fact that they're both nice round numbers and thought 'Hmm... Factor 6=1, 2, 3, 6...reciprocal numbers look good, so decided on a 20ft wide square, and checked remainder (20 for one side + 20 for the other = 40, 40 from 100 = 60, 60 divided by 2 <for each side> = 30ft), giving me a 30ft opposite side, then do the math (it's pretty quick) 20x30= (2x3=6 + 100) is 600 sqr ft.

Hope that helps, and you have a great day!