You cannot directly subtract the given values because their units are different. To be consistent, let's convert kilograms to grams with the conversion that 1,000 g = 1 kg.
43.278 kg(1,000 g/1 kg) - 28.1 g = 43249.9 grams
In subtraction, you will base the number of significant figures to the least of the given data. Since 28.1 has 3 significant figures, the answer should also contain 3 significant figures. Thus, it is much more convenient to report it in terms of kilograms.
43249.9 grams * 1 kg/ 1,000 g = 43.2 kg
