You can submit any of the following:

But always be sure that the file name you use for the submission has an extension correctly reflecting the file type (.pdf, .txt, .doc, .docx, etc.). I personally find plain text and PDF to be the most convenient formats to view, but I can also manage with .doc or .docx, and some TAs may favor doc/docx for ease of placing electronic markup in the document. (If the TA does not insert markup, it also generally works pretty well to just make side comments in Sakai.) Occasionally, students also have found ExCEL spreadsheets convenient for submitting something in tabular format. Other more obscure formats should be converted into one of the formats already mentioned.

Here is what I suggest for how to type mathematics in plain text (based on the way that math is done in LaTeX). I will give a few rules, and then some examples.

To make the points so far concrete, you might say something like the Pythagorean theorem is that $a^2+b^2=c^2$ or that a handy rule about exponentiation is that $b^x \cdot b^y$ is equal to $b^{x+y}$. (In LaTeX notation, we use that last expression rather than $b^(x+y)$, because the carat should be viewed as something that makes a superscript out of the the next symbol or the next chunk in curly braces. Superscripts can be used for things besides exponentiation, and the carat is not just an exponentiation operator.)

Just like \cdot is the LaTeX notation for a centered dot, anything that begins with a backslash is some sort of a command name, so you can use or make up other sensible things, for example \sum for the capital Sigma that introduces a summation, \prod for a product, \alpha and so on for Greek letters, \forall and \exists for quantifiers in logical expressions, \vee and \wedge for the OR and AND symbols, \implies for the logical implication symbol, \cup and \cap for set union and intersection. I think that's most of what you might need, except that a couple commands with arguments could be useful, for example, "\overbar{x}" to put a bar over "x".