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[a]

This is in hours
for minutes and seconds
.1047 hours x 60 minutes/hour = 6.284 minutes
.284 minutes x 60 seconds/minute = 17 seconds
so the time is 6 minutes 17 seconds
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twice the diameter would be 16 miles or 2*8 miles

that's because (2*8) * (2*8) * (2*8) = (2*2*2) * (8*8*8)
[b]

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notice the difference between [a] (the 2nd line) and [b]
the difference is the factor

so if you double the diameter this is the factor you multiply the time by
to get the new time.