Atractor company decides to reduce the mass of its tractor by 100 kg. the new tractor design is identical to the old design in everything other than weight. compare the force it would take to move the old tractor to the force it would take to move the new tractor.

The result that should be established is in the form
y = f(x) 
where x, the amount of sunlight is the controlled (independent) variable,
y =  height (growth) that corresponds to the amount of sunlight. Therefore y depends on x.

Clearly,
x, the amount of sunlight is the independent variable. It can be controlled.
y, the measured amount of growth is the dependent variable.

The independent variable is the amount of sunlight.
The dependent variable is the growth.