Question 1092822
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Let "x" be the number of atoms of oxygen.
Then the number of atoms of hydrogen is 3x,
and the number of atoms of carbon is 3x+4.


Collecting altogether, we obtain


H  + O +   C    = 18
3x + x + (3x+4) = 18  ====>


7x + 4 = 18  ====>  7x = 18-4 = 14  ====>  x = {{{14/7}}} = 2.


Then the answer is:  H   O   C
                      6   2   10.

The chemical formula {{{C[10]H[6]O[2]}}}.

                     Naphthoquinone    ( From Wikipedia  https://www.algebra.com/tutors/faq.mpl ) 
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