On adult.csv data set: 1. calculate the average age and number of rows for the 4 groups (sex, income) and join the corresponding 2 values to each row in the group; 2. extract people with age between 20 and 40 and working in a work group starting with "S" and people with age between 40 and 60 and working in the Private sector (workclass starts with "P"). Put both groups in a single data table.