chrystal jogs from her house to school, a distance of 6.8 miles, at a constant rate of 4.2 miles per hour. If x represents the amount of time (in hours) since chrystal leaves her house, which formula represents chrystal's distance y (in miles) from school in terms of the amount of time since she left her house

school starts out 6.8 miles away, and the distance decreases with each hour. So,

y = 6.8 - 4.2x