Need to know which formula to use. List the values I would insert into equation and final answer

A head librarian supervises a number of libraries in a large county. He wants to know if full-time library workers and part-time library workers re-shelve books at the same rate. So, he checks the records of 35 full-time library workers and finds that they re-shelve an average of 190 books per hour with a standard deviation of 18.3 books per hour. The records of 35 part-time library show that they re-shelve an average of 180 books per hour with a standard deviation of 14.4 books per hour. Using a level of significance of a=.05, is there enough evidence to indicate a difference in the mean number of books re- shelved by full-time workers compared to part-time workers? Answer the following questions: 1. Multiple choice: Which equation would you use to solve this problem? A. (X1 - X2) - Z $1 52 +