Joe is interested in observing how the height of a ramp affects the speed of his toy car when he releases it at the top of the ramp. He sets up 3 ramps, one at a 15 cm from the ground, one at 20 cm, and one at 25 cm. He then times how long his car takes to travel a specific distance from the time he releases it. He determines that the car has the greatest speed when the ramp is 20 cm off the ground. Use this information to answer Questions 6-8 below:
6.
What is the independent variable in this experiment?

7.
What is the dependent variable in this experiment?

8.
How many treatments did Joe have?