A bank's risk analyst is in charge of offering credit to people with good credit histories. Suppose that Chase Bank is predicting how much debt a person will accrue on a new credit card (in $) as a function of their credit score (a number between 300 and 850, measured in credit score units). A person with a credit score of 400 credit units averages a debt of about $9,000 and a person with a credit score of 700 credit units averages a debt of about $2,500. Calculate the rate of change. Provide a numerical answer (do not use units). Round to the nearest whole number.