47.82 is rounded to 47.8 because the '2' in the hundredths column means you round down. The same goes for 74.31- it becomes 74.3 because the '1' in the hundredths column means you round down.
To get this answer you can divide 321 and 12. But that will give you an uneven number such as 26.75. And because you cant have 26.7 tables you will wound it up to be 27 tables.