A company that manufactures electronic calculators uses a certain type of plastic . An alternative plastic material is introduced in the market and the manager of the company is thinking of shifting to this material . He will decide to shift if the mean breaking strength of the new material is greater than 155. It is known that the breaking strengths of the new plastic material follow the normal distribution and have a standard deviation of 10 psi ( pounds per square inch). Six samples of the new plastic materials were randomly selected and their breaking strengths were determined. The data obtained were 156, 154, 168157160 and 158. Estimate the true mean breaking strength of the new plastic material and measure the precision of this estimate.