A researcher knew that before cellphones, a person made on average 3.5 calls per day. He believes that the number of calls made per day today is higher. He selects a random sample of 35 individuals who use a cell phone. He asks them to keep track of the number of calls that they made on a certain day and the mean was found to be 3.9 calls. Using 5% level of significance, is there enough evidence to support the researcher's claim? The standard deviation for the population found by a previous study is 0.90.

a. State the hypothesis statements; the type and direction of the test.

b. Write down the underlying assumptions required to carry out the test.

c. Calculate the test statistic.

d. Obtain the p-value for the test.