Since we’re asked for a whole number, we count the number of zeros after the first nonzero numbers. In this case, our first non-zero numbers are 2 and 4 (24). The number of zeros after these numbers are four (4). The number of zeros indicates the power number of 10.
Had we been asked for a decimal number and a power of 10, then the answer would have been 2.4 * 10^5