Julissa is running a 10 -kilometer race at a constant pace. After running for 18 minutes, she completes 2 kilometers. After running for 54 minutes, she completes 6 kilometers. Her trainer writes an equation letting t , the time in minutes, represent the independent variable and k , the number of kilometers, represent the dependent variable. Which equation can be used to represent k , the number of kilometers Julissa runs in t minutes?