Question 9 (5 points) Listen Tables Researchers want to study noise levels produced by vehicles on a busy street. Assuming the variable is approximately normally distributed, the mean noise level for 15 vehicles was 84.5 decibels, with a standard deviation 3.3 decibels. a) What distribution should be used, z or t? Type z or t in the answer box. [1 mark] b) Find the critical Value for the 80% confidence interval. Write exact value from the table. [2 marks] c) Find margin of error rounded to two decimal places. For example, 2.22 [1 mark] d) Find the 80% confidence interval of the true mean. Round answers to two decimal places and separate the lower and upper limits of the interval with a comma and no space. For example: 10.13, 12.64 [1 mark] A/ A/