"I can't say what you don't know. This is something that I know very well."
"But you know everything," she murmured.
Without seeking to deny this, Queed said: "It tells you right there in the book."
"I don't see it," said Fifi, nervously looking high and low, not only in the book but all over the room.
The young man fell back on the inductive method: "What is that six then?"
"Oh! Now I see. It's the difference in the number of days consumed—isn't it?"
"Naturally. Now put down your equation. No, no! The greater the rate of progress, the fewer the number of days. Do not attempt to subtract the greater from the less."
Now Fifi figured swimmingly:—
(105/(x-2)) - (105/x) = 6
105x - 105x + 210 = 6x^2 - 12x
6x^2 - 12x - 210 = 0
6x^2 - 12x - 210 = 0
x^2 - 2x - 35 = 0
(x - 7) (X + 5) = 0
x = 7 or -5
She smiled straight into his eyes, sweetly and fearlessly. "Seven! Just what you said! Oh, if I could only do them like you! I'm ever and ever so much obliged, Mr. Queed—and now I can go to bed."