An article reports an investigation into the toxicity of bilirubin on several cell lines. Ten sets of human liver cells and 20 sets of mouse fibroblast cells were placed into solutions of bilirubin in albumin with a 1.4 bilirubin/albumin molar ratio for 24 hours. In the 10 sets of human liver cells, the average percentage of cells surviving was 53.9 with a standard deviation of 10.7. In the 20 sets of mouse fibroblast cells, the average percentage of cells surviving was 73.1 with a standard deviation of 9.1. Let my represent the population mean for the mouse cells and let My represent the population mean for the human cells. Find a 98% confidence interval for the difference My - My . Round down the degrees of freedom to the nearest integer and round the answers to three decimal places. The 98% confidence interval is (