Ourth Amendment forbids only Unreasonablesearches and seizures

After overhearing from a public telephone what appeared to be arrangements for a drug transaction, a police officer followed the defendants car. When the driver committed a tracfic violation, the officer stopped his car. The officer told the driver that he believed that he was carring narcotices in his car and asked for consent to search the car. The driver said that he had noting to hide. Indeed, having gotten consent, the officer opened the door on the passenger side and saw a folded brown paper bag on the floor of the car. The officer picked up the bag, opened it, and found cocaine inside.
Did the consent to search the car authorize opening the brown paper bag? Explain.
Should the evidence be permitted for use against the defendant? Why or why not?