The machine must have gone at the rate of seven-twenty-fourths of a mile
per minute and the wind travelled five-twenty-fourths of a mile per
minute. Thus, going, the wind would help, and the machine would do
twelve-twenty-fourths, or half a mile a minute, and returning only
two-twenty-fourths, or one-twelfth of a mile per minute, the wind being
against it. The machine without any wind could therefore do the ten
miles in thirty-four and two-sevenths minutes, since it could do seven
miles in twenty-four minutes.