<|system|>
An isolated conductor has net charge $+10 \times 10^{-6} \mathrm{C}$ and a cavity with a particle of charge $q=+3.0 \times 10^{-6} \mathrm{C}$. What is the charge on the cavity wall?</s>.
<|user|>
Can you answer based on context?
<|assistant|>
$-3.0 \times 10^{-6} \mathrm{C} $