100.80 kg - 20.35 kg = 80.45 kg . . . . the new weight of the bag
It's a pretty straightforward subtraction problem. As with any decimal addition or subtraction, you line up the decimal points and extend any numbers with zeros to make the number of decimal places match.
12 inches make a foot, therefore the scale model is 1/21 the size of the actual if you're using the information given above. so the wingspan should be 10
