Final answer:
Using the formula P=2l+2w, we can solve for either length (l) or width (w) given the perimeter and the other dimension.
Step-by-step explanation:
The formula for the perimeter of a rectangle is P=2l+2w, which involves the perimeter (P), the length (l), and the width (w). Given this formula, if we know the value of the perimeter and one of the other two dimensions, we can solve for the remaining unknown dimension. Therefore, if perimeter is known, we can solve for either l or w, but not both simultaneously without additional information. The equation for a rectangle's perimeter allows us to calculate both length and width when one of those and the perimeter is already known.