Short Answer: Because the exam is for version R80, the correct answer is 3 months.
Long Answer: When Hit Counts were introduced in R75.40, default value was 6 months. However this default got changed to 3 months somewhere in R77.XX (I know for sure the default in R77.30 is 3 months), so any reasonably new installations will be set to 3 months. However any SMS installations that existed in R75.4X and were upgraded/imported into a later version will still be set to that original default of 6 months, unless someone manually changed it.
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