Create a table to represent the make up of the 113th Congress like the table on page 87 (table 4.3) of Policy Practice for Social Workers.
You do not need to calculate the last column percent of underrepresentation. You may need to consult the sources at the bottom of table 4.3 to get ideas. Look in Congressional Research Center and you can Google questions like "How many women are in Congress?"
Without access to the ebook that is being used in your class, we cannot see exactly what the table that you are referring to includes. However, since you are talking about underrepresentation, it is likely that the table looks at the percentage of women and of various minorities in the Congress. If you follow the link below, you will be able to find a great deal of information on the demographic makeup of the 113th Congress (the Congress that is now sitting).
Since your question specifically mentions women, let us examine the information given on female members of Congress. The link specifies that 20 out of the 100 Senators are female. Among the 435 Representatives in the House, there are 77 women. In both houses, the majority of the female members are Democrats.
Looking at racial minorities, we can see that there are only 2 African American Senators (again, out of 100). There are 40 African American Representatives in the House. All of the African Americans in the House are Democrats. Hispanics are the fastest-growing minority in the United States. However, they are also underrepresented in Congress. In the 113th Congress, there are 3 Hispanic Senators and 28 Hispanic Representatives.
These are the categories that you are most likely to need to include in your table. The next step for you would be to look at the table in your book and use these figures to make a table of your own.