The owner at Kim’s Home Interiors is reviewing the sales records of two managers who are up for promotion, Katie and Stella, who work in different stores. At Katie’s store, the mean sales have been $23,200 per month, with a standard deviation of $2170. At Stella’s store, the mean sales have been $25,600 per month, with a standard deviation of $2300. Last month, Katie’s store sales were $28,408 and Stella’s store sales were $29,510. At both stores, the distribution of monthly sales is normal. 

(a) Convert last month’s sales for Katie’s store and for Stella’s store to z-scores. Katie: 

(b) If one of the two were to be promoted based solely on the sales last month, who should be promoted? Explain.