I sat down, worked it out hastily on the back of an envelope, and made it a yard and a half.
"No," said Herbert; "I know it's 'four cows,' but I can't get it."
"Sorry," I said, "how stupid of me; I left out the table-money."
I did it hastily again and made it three minutes twenty-five seconds.
"It is difficult, isn't it?" said Herbert. "I thought, as you used to be mathematical and as I'd promised the girl—"
"Wait a moment," I said, still busy with my envelope. "I forgot the subaltern. Ah, that's right. The answer is a hundred and twenty-five men…. No, that's wrong—I never doubled the half-crown. Er—oh, look here, Herbert, I'm rather busy this morning. I'll send it to you."
"Right," said Herbert. "I know I can depend on you, because you're mathematical." And he opened the door for me.
I had meant to do a very important piece of work that day, but I couldn't get my mind off Herbert's wretched problem. Happening to see Carey at teatime, I mentioned it to him.
"Ah," said Carey profoundly. "H'm. Have you tried it with an 'x'?"
"Of course."