Length is the independent variable while P is the dependent variable.
Independent variables are variables that can stand alone while dependent are depend on others.
Independent variables are input variables of a function whole independent are the output variables of a function.
Given the function as shown:
P = 2l + 20
length is the independent variable while P is the dependentw variable.
Learn more on independent and dependent variables here; https://brainly.com/question/25223322