Test the claimed bulb power and change the sample size

A manufacturer makes light bulbs with power normally distributed with mean 13 watts and standard deviation 2.716 watts. A sample of 50 bulbs has mean power 13.168 watts.

(i) Test at the 5% significance level whether the manufacturer is understating the mean power.

(ii) Explain “a 5% level of significance” in this context.

(iii) At the 10% significance level, what is the least sample size for concluding that the manufacturer has understated the mean power?