Answer: 13.827 days (approximate)
A more accurate value would be 13.8271643518519
Round it however you need to.
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Step-by-step explanation:
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds
Let's see how many seconds there are in a day.

I set up those fractions so that the units "day", "hours", "minutes" cancel out. The only unit left over is "seconds".
There are exactly 86,400 seconds in 1 day.
This leads to the fact the sink fills up at a rate of 86,400 drops per day, since the leak rate is 1 drop per second.
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1 drop = 0.003 cubic inches approximately
x of those drops give a volume of 0.003x cubic inches, where x is some positive whole number. Set this equal to the volume of the sink and solve for x.
0.003x = 3584
x = 3584/0.003
x = 1,194,666.66666667 approximately
Round up to the nearest whole number to get 1,194,667
The sink starts to overflow when we have 1,194,667 drops of water in it.
Divide this over 86,400 mentioned earlier.
(1,194,667)/(86,400) = 13.8271643518519 approximately.
Round that however you need to. If for instance you round to 3 decimal places, then it would be 13.827