Robinson a large department store wanted to example tolook at which credit cards

Robinson a large department store wanted to example tolook at which credit cards were being utilized for purchases. Asample of 18 credit card sales was taken and recorded. The amountscharged for each of three different credit cards MasterCard Visaand Discover were: six MasterCard sales seven Visa sales andfive Discover sales. The store used an ANOVA to test if the meansales for each credit card were equal. What are the degrees offreedom for the F statistic?