A college career officer wonders if the employment fields of graduates are more directly related to field

Question:

A college career officer wonders if the employment fields of graduates are more directly related to field of study for some majors than for others. She collects data on majors and jobs for 400 of the most recently employed graduates. Here is what she finds. Of the 240 who were employed in a field related to their majors, 48 were business majors, 49 were humanities majors, 96 were social science majors, and 47 were science majors. Of the 160 who were employed in a field not related to their major, 32 were business majors, 51 were humanities majors, 64 were social science majors, and 13 were science majors.
a. What are the variables in this study?
b. State the null hypothesis.
c. What is the df for this study?
d. Complete the following table. Use row and columns totals to compute expected frequencies. Put the expected frequencies in parentheses.