Advertisers fear that users of DVRs (digital video recorders) will "fast forward" past commercials when they watch a recorded program. A leading British pay television company told its advertisers that this effect might be offset because DVR users watch more TV. A sample of 20 DVR users showed a daily mean screen time of 2 hours and 31 minutes with a standard deviation of 14 minutes, compared with a daily mean of 2 hours and 14 minutes with a standard deviation of 12 minutes for a sample of 20 non-DVR users.

(a-1)Construct a 99 percent confidence interval for the difference in mean TV watching.(Round your answers to 2 decimal places.)

The 99% confidence interval is fromto

My answer is still wrong..confused with the formula