12 Write the expression with positive exponents. \( \frac{9 a^{-2} c^{9}}{b^{6}} \)

To rewrite the expression \( \frac{9 a^{-2} c^{9}}{b^{6}} \) with positive exponents, you can apply the rule that \( x^{-n} = \frac{1}{x^n} \). Thus, the term \( a^{-2} \) is converted to \( \frac{1}{a^2} \). So, the expression becomes: \[ 9 \cdot c^9 \cdot \frac{1}{a^2} \cdot \frac{1}{b^6} = \frac{9 c^{9}}{a^{2} b^{6}}. \] Now, you've got your expression with all positive exponents: \( \frac{9 c^{9}}{a^{2} b^{6}} \).