If you are adept with SQL, you can write a SQL query as a string and pass it to the read_sql_query function. For example, the following will reproduce the output from step 4:

>>> sql_string1 = '''
    select 
        Name, 
        time(avg(Milliseconds) / 1000, 'unixepoch') as avg_time
    from (
            select 
                g.Name, 
                t.Milliseconds
            from 
                genres as g 
            join
                tracks as t
                on 
                    g.genreid == t.genreid
         )
    group by 
        Name
    order by 
         avg_time
'''
>>> pd.read_sql_query(sql_string1, engine)

To reproduce the answer from step 6, use the following SQL query:

>>> sql_string2 = '''
    select 
          c.customerid, 
          c.FirstName, 
          c.LastName, 
          sum(ii.quantity * ii.unitprice) as Total
    from
         customers as c
    join
         invoices as i
              on c.customerid = i.customerid
    join
        invoice_items as ii
              on i.invoiceid = ii.invoiceid
    group by
        c.customerid, c.FirstName, c.LastName
    order by
        Total desc
'''
>>> pd.read_sql_query(sql_string2, engine)