Hypothesis test for single mean

Choo Paper Company makes various types of paper products. One of their products is a 30 mils thick paper. In order to ensure that the thickness of the paper meets the 30 mils specification, random cuts of paper are selected and the thickness of each cut is measured. A sample of 256 cuts had a mean thickness of 30.3 mils with a standard deviation of 4 mils.
a. work out the standard error of the mean.
b. At 95 percent confidence using the critical value approach, test to see if the mean thickness is significance more than 30 mils.
c. Show the p -value approach results in the same conclusion as that of part b.