If the government has decided that tossed orange peels impose a negative on the public that must be rectified by imposing a $4 per bag, then the new equilibrium price is,
p* = $9 ( when the quantity of bag is 1)
In that time the new equilibrium quantity is, q* = 5 bag(s).
If the new equilibrium quantity (5) is the optimal quantity, before some bags were oranges being overproduced that is,
q* = 1 bag(s)