A 10 mW signal after a 24 dB gain is a 2500 mW signal.
10 mW x 10 x 10 x 10 / 2 / 2 = 2500 mW = 2.5 Watts
It is common to see the product of two gains expressed as the "sum" of the gains, as in 3 dB + 3 dB = 6 dB. At least we can remind ourselves that in this convention "+" means "combine via multiplication".
The good news is that The CWNP Program is agnostic and doesn't test what you think about decibel numbers or whether you add them or multiply them, only that you can select the correct numerical answer out of a list. The answers are typically whole numbers and the rules of 10's and 3's almost always help.
I hope this helps. Thanks. /criss