A car manufacturer is interested to test a new engine to determine whether it meets air environmental pollution standards which require that the mean emission be less than 20 parts of carbon. Ten engines are selected and their level of emission is described in table.

A) Please conduct a test of null hypothesis that the engine's mean emission equals 20 with the alternative hypothesis being means' value below 18, with alpha=0.05

B) Please construct a 95% confidence interval for the mean emission level and write in English its interpretation.

15.6

16.2

22.5

20.5

16.4

19.4

19.6

17.9

12.7

14.9