A sales manager for an advertising agency believes there is a relationship between the number of contacts that a salesperson makes and the amount of sales dollars earned. A regression analysis shows the following results: Coefficients Standard Error t Stat p value Intercept -12.201 6.560 -1.860 0.100 Number of contacts 2.195 0.176 12.505 0.000 ANOVA df SS MS F Significance F Regression 1.00 13555.42 13555.42 156.38 0.00 Residual 8.00 693.48 86.68 Total 9.00 14248.90 X=33.4 ∑(X−X)2=2814.4. Rounding to one decimal place, the 95% confidence interval for 30 calls is .

a.55.8, 51.5
b.51.4, 55.9
c.46.7, 60.6
d.31.1, 76.2