Question 1091416
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<pre>
Instead of using formulas, I prepared this Table below to provide better visual presentation.


	-26	Initial level
		
n	day	night
---------------------
1	-18	-20
2	-12	-14
3	-6	-8
4	 0	      <<<---=== Just at the surface !


<U>Answer</U>. 4 days.
</pre>

Thanks are due to my MS Excel in my computer.