You would have to buy Word. The cheapest way is as part of Works Suite, or
check for student versions of Office or see if your school has a special
deal.
However, WordPerfect will let you save your documents as RTF, which your
teacher will be able to open. WordPerfect might even let you save your
documents as Word. Check the options in the Save dialog, or check
WordPerfect Help.
DM