Given the task definition and input, reply with output. In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.

Dr. Spencer Reid: Long - term stranger abductions of children Billie 's age are rare . They represent only half of one percent of all missing cases per year . But they are usually more likely to be fatal . Of the children that are abducted and murdered , 44% die within the first hour . From that point forth , their odds of survival greatly decrease . 75% are gone after three hours . Virtually all of them are dead after _ twenty _ - four .
Aaron Hotchner: Which means we have just under four hours to find her .
hours