Answer:
The correct answer is 6.
Explanation:
When using a decimal after a whole number, all numbers are seen as significant as the number cannot be recognized without them.
Example: 13,436,000 mm would only have five significant numbers as there is no decimal and the number can still be recognized without the extra zeros.
However, 13,436.000 has eight significant numbers, as the decimals are needed to see that the number has a decimal point into the thousandths.
Hope this helps!