Call the number  is x, with x is the 2 - digit number, called \(\overline{xy}\). We have :

\(\overline{xy}+x+y=\overline{xy}+\dfrac{1}{3}\times\overline{xy}\), which \(\overline{xy}⋮3\)

=> \(\overline{xy\in}\left\{12,15,18,21,24,...\right\}\)

1/3 of 12 is 4  => 12  => 12 + 1 + 2 = 15 => 12 + 4 = 16 => 16 > 15(elminate)

.. 15 is 5 => 15 => 15 + 1 + 5 = 21 => 15 + 5 = 20 => 21> 20 (elminate)

... 18 .. 6 => 18 => 18 + 1 + 8 = 27 => 18 +6 = 24 => 27 > 24 (elminate )

.. 21 .. 7 => 21 => 21 + 2 +1 = 24 => 21 +7 = 28 => 24 < 28 (elminate )

... 24 .. 8 => 24 => 24 + 2+ 4 = 30 => 24 + 8 = 32 => 30 < 32 (elminate)

... 27 .. 9 => 27 => 27 + 2 + 7 = 36 => 27 + 9 = 27 + 2 + 7 because 9 = 2 + 7 ( possible )

So the number is 27