Carl is boarding a plane. he has 222 checked bags of equal weight and a backpack that weighs 4kg. the total weight of carl's baggage is 35kg

Well first of all, 'kg' means mass, not weight.

If the total mass of all his baggage is 35 kg, and the mass
of his backpack is 4 kg, then the combined mass of all of his
checked bags is  (35 - 4)  =  31 kg.

If all of his checked bags have the same mass, then the mass
of each one is

                        (31 kg / 222 bags)  =  139.64  grams/bag   (rounded)

In this problem it decreased 20%