Find number abc

One day while doing door-to-door market research, this guy knocks on a door and is greeted by a beautiful young housewife.
"Hello," he starts, "I'm doing some research for a petroleum jelly manufacturer. Have you ever used the product?"
"Yes. My husband and I use it during sex," she answers.
The researcher is taken aback. "Um, er, I admire you for your honesty," he continues. "Can you tell me exactly how you use it?"
"Sure, we put it on the doorknob so the kids can't get in."