What is the independent variable?
What is the dependent variable?

Answer:
the independent is the age of the tree and the dependent is the diameter
Explanation:
the diamter of the tree is based off of the age as we can see that it gets bigger the older the tree is
Answer: Independent variable: age of the tree (years), Dependent variable: tree diameter (mm)
The diameter of the tree is dependent on what age the tree is. As the tree gets older, the diameter increases. The dependent variable depends/relies on the value(s) of the independent variable.