Barbara, Mark, and Carlos participated in the third heat of “The Big Race”. Barbara thought she could win with a 3 meter head start even though she only pedaled meters every 2 seconds. Mark began at the starting line and finished the -meter race in 5 seconds. Meanwhile, Carlos rode his tricycle so that his distance from the starting line in meters could be represented by the equation , where x represents time in seconds. What is the dependent variable? What is the independent variable?