Answer:3.5 days is awfully precise and waxing gibbous is awfully vague.Let’s just make sure we understand our terminology. Waxing means getting fatter and gibbous means fat. A waxing gibbous moon lasts for approximately 7 days from the first quarter phase right up to the full moon phase.By 3.5 days I’m assuming you mean half a week and simplifying the lunar phases to 28 days exactly.So we have:Day 0 New moon.Day 7 First quarter.Day 14 Full moon.Day 21 Third quarter.Day 28 New Moon.Between day 0 - 7 we have the waxing crescent phase.Between day 7–14 we have the waxing gibbous phase.Between day 14–21 we have the waning gibbous phase.Between day 21–28 we have the waning crescent phase.So 3.5 days from day 7 would take us to day 10.5 which would still leave us in the waxing gibbous phase. 3.5 days after day 10.5 would take us to the full moon or over into the waning gibbous phase since the full moon lasts only an instant.
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