This is a really fun challenge. You have to figure out two problems: adding a column and adding a row. First, sit down with pen and paper and strategize. It would be a mistake to start writing code without a clear plan of how to do each.
Hint: For adding a column or a row, you need to append
new <td>s to the page. The question is how many.
How can you use a loop to add as many as you need?