The following data pertain to activity and costs for two recent months August September Activity level in units 16,000 20,000 Variable costs S12,000 17,000 14,000 S43,000 Fixed costs Total costs S48,000 Assuming that these activity levels are within the relevant range, the mixed costs for September were O a. $15,000 O b. $16,000 C. $22,000 O d. $47,000