well let me break it down for you
body fat is stored energy
1 lb of body fat contains 3500 calories worth of energy
in order to lose body fat, you must use it for energy. in order to this you must create a caloric defecit. where some of what the body uses every day will be metabolized from body fat.
lets say bob has 15 lbs of body fat in that picture. 15 lb of fat = 52,500 calories worth of energy.
if he is 5 weeks out, that means he is 35 days out.
if he has 35 days to drop 15 lbs of body fat, that means every day his body must burn , on average, 1500 calories of stored body fat.

not that tough to figure out