The expression you provided is:

$m^3 \cdot n^{-9}$

To simplify this expression so that it contains only positive exponents, we need to rewrite the term with the negative exponent. The rule is that a term with a negative exponent moves to the denominator and the exponent becomes positive.

Thus:

$m^3 \cdot n^{-9} = \frac{m^3}{n^9}$

This is the simplified form, with only positive exponents.

Let me know if you'd like further details or have any questions about this! Here are a few related questions that could help deepen your understanding:

1. How do you handle negative exponents in a fraction?
2. What is the rule for multiplying terms with exponents?
3. How do you simplify expressions that involve both positive and negative exponents?
4. Can you simplify an expression involving multiple negative exponents?
5. How does the distributive property work when exponents are involved?

Tip: Remember that any base with a negative exponent should move across the fraction line to the opposite side (numerator to denominator, or vice versa).