Answer:
-$860
-58.64%
Step-by-step explanation:
Given the cash price as $2200, the down payment as $500 and monthly installments of $320 for 8 months, the interest charged is calculated as;

Hence, the interest charged is $860
#Flat rate of interest is similar to simple interest rate.
Knowing n=8 months and interest as $860, the rate is calculated as:

Hence, the flat rate of interest over the 8 months is 58.64%