The traffic commissioner wants to know the average speed of all vehicles driving on River Rd. Police use radar to observe the speeds for a sample of 20 vehicles on River Rd. For the vehicles in the sample, the average speed is 31.3 miles per hour with standard deviation 7.0 mph. Construct and interpret a 98% confidence interval estimate of the true population average speed of all vehicles on River Rd. Use a 98% confidence level.