\(\begin{array}{l} + )\,\,\,\overline {23x4} \,\,\,chia\,\,\,het\,\,cho\,\,\,3\\ Ta\,\,\,co:\,\,\,2 + 3 + x + 4 = 9 + x\\ \Rightarrow \,\overline {23x4} \,\,\,chia\,\,\,het\,\,cho\,\,\,3 \Leftrightarrow \left( {9 + x} \right)\,\, \vdots \,\,3\\ \Rightarrow \left[ \begin{array}{l} 9 + x = 9\\ 9 + x = 12\\ 9 + x = 15\\ 9 + x = 18 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} x = 0\\ x = 3\\ x = 6\\ x = 9 \end{array} \right.\\ \Rightarrow x \in \left\{ {0;\,\,3;\,\,6;\,\,9} \right\}.\\ + )\,\,\,\overline {563x} \,\,\,chia\,\,het\,\,\,cho\,\,\,9\\ Ta\,\,\,\,co:\,\,\,5 + 6 + 3 + x = 14 + x\,\,\\ \Rightarrow \overline {563x} \,\,\,chia\,\,het\,\,\,cho\,\,\,9 \Leftrightarrow \left( {14 + x} \right)\,\, \vdots \,\,9\\ \Leftrightarrow \left[ \begin{array}{l} 14 + x = 18\\ 14 + x = 27 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} x = 4\\ x = 13\,\,\,\left( {ktm} \right) \end{array} \right.\\ Vay\,\,\,x = 4.\\ + )\,\,\,\overline {73xy} \,\,\,chia\,\,\,het\,\,\,cho\,\,\,5\,\,\,\,va\,\,\,9\\ \Rightarrow \overline {73xy} \,\,\,chia\,\,\,het\,\,\,cho\,\,\,5\\ \Rightarrow y = 0\,\,hoac\,\,\,y = 5.\\ + )\,\,\,Voi\,\,\,y = 5 \Rightarrow \overline {73x5} \\ co\,\,7 + 3 + x + 5 = x + 15 \Rightarrow \overline {73x5} \,\,\,chia\,\,\,het\,\,\,cho\,\,\,9\\ \Leftrightarrow \left[ \begin{array}{l} x + 15 = 18\\ x + 15 = 27 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} x = 3\\ x = 12\,\,\,\left( {ktm} \right) \end{array} \right.\\ \Rightarrow x = 3.\\ + )\,\,Voi\,\,y = 0 \Rightarrow \overline {73x5} \\ co\,\,7 + 3 + x + 0 = x + 10 \Rightarrow \overline {73x0} \,\,\,chia\,\,\,het\,\,\,cho\,\,\,9\\ \Leftrightarrow x + 10 = 18\\ \Leftrightarrow x = 8\\ \Rightarrow x = 8.\\ Vay\,\,so\,\,\,can\,\,tim:\,\,\,7380\,\,hoac\,\,\,7335. \end{array}\) Các câu còn lại bạn làm tương tự nhé!!!