Read what it says in the link:
"Trailing zeros in large integers are always counted by this script. An example will make this clear. The number 545100 shall be written in scientific notation
with six significant digits as 5.45100e5
with five significant digits as 5.4510e5
with four significant digits as 5.451e5
If it is written as 545100 then it is impossible to know how many significant digits there are in it. This script counts all trailing zeros if you do not use scientific notation."
It is not possible to know whether the 00 in the 2400 are genuinely zeroes, as they would be if the actual number is, for example, 2400.123 or whether they have been rounded off from, for example, 2419.622.
So both are "correct" and the question is undecidable without further information.
Mind, your teacher probably wants you to give the answer 2 and will mark you down if you say 4 no matter how loudly you call him a fascist.