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Based on a sample of women, researchers found that a woman's progesterone levels (measured in ng/mL) increase throughout the 40 weeks of pregnancy according to the regression equation below: progesterone = -0.63 + 2.92(weeks pregnant) If a woman is 18 weeks pregnant and has a progesterone level of 54.77 ng/ml, what is her residual? Round to two decimal places and do not include units