Final answer:
72,100 km has 4 significant figures: 7, 2, 1, and 0.
Step-by-step explanation:
Significant figures are the digits in a number that carry meaning in terms of its precision. In 72,100 km, there are 4 significant figures: 7, 2, 1, and 0. The zeros in the middle of the number are significant because they are between non-zero digits. However, trailing zeros after a decimal point are significant, but trailing zeros before a decimal point are not.