The perimeter of a rectangle is the sum of all its sides, so its 2 lengths + its 2 widths, or 2l + 2w.
So you need 2l + 2w to equal 8.
2l + 2w = 8.
You can divide both sides by 2.
l + w = 4.
So now it comes down to two positive numbers that add up to 4. You can have 3 and 1, 2 and 2, 1.5 and 2.5, etc.