Replace the question mark with a number

On a senior citizen bus tour, the driver was surprised. While the passengers were unloading, to do some sightseeing, one elderly lady stopped and whispered in his ear, "Driver, I believe that I was sexually harassed!"
The driver didn't think much of this complaint, but promised he would check into it soon.
Later, that very same day, as the passengers were unloading again, a second little old lady bent down and whispered in his ear, "Sir, I believe I was sexually harassed!"
This time, he knew it had to be taken care of soon. A few passengers had remained on the bus, and he decided to go back and question them, to see if they had any knowledge of what was going on.
He found one little old man crawling along the bus floor underneath the seats and stooped down to question him. "Excuse me, sir, could I help you?"
The elderly man looked up and said, "Well, sonny, you sure can. I've lost my toupee and I'm trying to find it. I thought I'd located it twice, but they were both parted in the middle, and mine's parted on the side!"