Use the following information to answer Questions $1-4$: In a competitive market for fresh lemonade, the market demand for $12-$ounce servings is QD $=10010$P and the market supply is QS $=15$P$.$

$[4]$ Now suppose that the production of lemonade caused a costly negative externality on innocent bystanders $($e$.$g$.,$ squirted acidic lemon juice in their eyes$).$ Given the externality, would the unregulated market price of lemonade from $[1]$ be efficient? If not, is it too high or too low?