The following data represent the time (minutes) it takes to drill an additional 5 feet from the depth indicated for both wet drilling and dry drilling conditions.

(a) Draw a scatter diagram, treating depth as the explanatory variable and time as the response variable, but use a different plotting symbol for wet and dry. For example, use a circle for wet and a square for dry.
(b) Find the least-squares regression equation y̅ = b0 + b1x1 + b2 x2, where x1 is depth and x2 = 0 for wet and x2 = 1 for dry.
(c) Test the hypotheses H0: b1 = 0 versus H1: b1 ≠ 0 and H0: b2 = 0 versus H1: b2 ≠ 0.
(d) Construct 95% confidence and prediction intervals for time to drill an additional 5 feet in dry conditions where drilling starts at 100 feet. Interpret the results.