An online stock trading company makes part of their revenue from clients when the clients trade stocks therefore, it is

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An online stock trading company makes part of their revenue from
clients when the clients trade stocks therefore, it is important to
the company to have an good idea of how many trades its clients are
making in a given year. In a sample of 120 clients of an online
stock trading company, the average number of trades per year was 82
with a standard deviation of 16. Assume you are to test the
hypothesis that the average number of trades per year is different
than the previous year when the average number of trades was 85 -
using the 5% level of significance.
State the null and alternative hypotheses. (is it one of
two-tailed?)
Using a 5% level of significance, what is your critical
value?
Please give me step-by-step instruction. I havent taken
Statistic in years.  
What is the value of the test statistic? What conclusion do you
make about the null hypothesis (reject/fail to reject?)