Two production designs are uses to manufacture a certain product. The mean time required to produce the product using the old design was 3.51 days with s = 0.79 days. The new design required an average of 3.32 days with s=0.73

days. Equal size samples of 150 were used for both designs. What would a 95 percent interval estimate of the difference between the mean times required to produce the product reveal about which design should be used?