Hi! Just need to note that the dependent variable depends on the independent variable. In this question, the aim is to find out if different wheels affect the speeds of the car. Thus, the speed of the car (dependent variable) depends on the type of wheels (Independent variable) that we use in the experiment. The controlled variables are the things we keep constant during the experiment so that they will not affect the results. Examples could include the length of the ramp, the height at which the car is released etc. Hope this helps :)