a 19. The company made a research that two kinds of nails are being compared for strength. They took thirty of each type of nails through the same wood by similar strength. Brand A had an average strength of 5.6cm with a standard deviation of 0.5cm. Brand B had an average strength of 7.1cm with a standard deviation of 1.2cm. Construct a 95% confidence interval for the difference of the population means