Help with math question?

Divide 1440 by 32. That gives you the amount of "man-days" of food. I presume the "ratio" is a measure of food needed per man. So since that goes up, then more food is needed for the same number of men, so the man-day figure must be divided by 3/2, which means that the new man-days total is 30. But you want to make that last for 40 days, so you must get to a total man "count" to accommodate that, so you multiply the original population by 30/40, to get to a new count of 1080 men, which means that 360 men would have to leave.