2015 AMC 10B Problem 3

Let the number written twice be $x$, and let the number written three times be $y$. Then $2x+3y=100$. If $x=28$, then $3y=100-56=44$, impossible for an integer $y$. Therefore $y=28$, and $2x=100-84=16$, so $x=8$. Thus, the correct answer is A.