9514 1404 393
Answer:
6.302×10^7 kg
Step-by-step explanation:
Since we want to find the difference in mass, we need to have the same exponent on both numbers. For that purpose, it is convenient to change the representation of the train's mass to 0.998×10^7 kg.
The carrier has more mass by the amount of ...
7.3×10^7 -0.998×10^7 = (7.300 -0.998)×10^7 = 6.302×10^7 . . . kg
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Your (scientific or graphing) calculator or a spreadsheet can figure this for you and give you the scientific notation display.