Calculate the number 6724

A young doctor had moved out to a small community to replace a doctor who was retiring. The older doctor suggested the young one accompany him on his rounds so the community could become used to a new doctor. At the first house a woman complained,
"I've been a little sick to my stomach."
The older doctor said, "Well, you've probably been overdoing the fresh fruit. Why don't you cut back on the amount you've been eating and see if that does the trick?"
As they left the younger man said, "You didn't even examine that woman. How'd you come to your diagnosis so quickly?"
"I didn't have to. You noticed I dropped my stethoscope on the floor in there? When I bent over to pick it up, I noticed a half dozen banana peels in the trash. That was what was probably making her sick."
"Hmmm," the younger doctor said, "Pretty clever. I think I'll try that at the next house."
Arriving at the next house, they spent several minutes talking with a younger woman. She complained that she just didn't have the energy she once did.
"I'm feeling terribly run down lately."
"You've probably been doing too much extra work for the church," the younger doctor told her. "Perhaps you should cut back a bit and see if that helps."
As they left, the elder doc said, Your diagnosis is almost certainly correct, but how did you arrive at it?
"Well, just like you did at the last house, I dropped my stethoscope and when I bent down to retrieve it, I noticed the preacher under the bed."