Calculate the number 9157

He'd decorated it with expensive, heavy oak furniture, a collection of costly art posters, and various other accoutrements to impress any potential client who walked through the door.
He'd placed ads and sent out engraved announcements about his new business, and he was sitting back waiting for the phone to ring or his first client to appear.
Suddenly he heard the elevator doors closing and footsteps coming down the hall toward his office.
He wanted to give the impression of a successful professional, so he grabbed the shiny new phone receiver and plunged into imaginary conversation. 'Yes, Mr. Torrence,' he intoned as the stranger entered the office, 'I'll attend to that business as soon as I've a free minute. I'm sure you're aware that Mr. Hollings had wanted me to handle his estate. I had to put him off, since I'm far too busy with other cases, but I'll manage to sandwich yours between the others somehow. Yes, yes, certainly, it's my pleasure, sir. Goodbye.'
Certain that he had properly impressed his prospective client, he hung up the receiver and turned to face the stranger, who was patiently waiting. 'Excuse me, sir,' said the man, 'I've come to connect your telephone.'