MATH PUZZLE: Can you replace...

A man went to a psychiatrist for his phobia.
"Doc," he said, "I've got trouble. Every time I get into bed, I think there's somebody under it. I get under the bed, I think there's somebody on top of it. Top, under, top, under. You gotta help me, I'm going crazy!"
"Just put yourself in my hands for two years," said the shrink, "Come to me three times a week, and I'll cure your fears."
"How much do you charge?"
"A hundred dollars per visit."
"I'll sleep on it," said the man.
Six months later the doctor met the man on the street.
"Why didn't you ever come to see me again?" asked the psychiatrist.
"For a hundred buck's a visit? A bartender cured me for ten dollars."
"Is that so! How?"
"He told me to cut the legs off the bed!"