Có bao nhiêu số tự nhiên dạng \(\overline {5a42b} \) chia hết cho cả \(2;5\) và \(3?\)

\(\left( {a + b} \right) \in \left\{ {9;18} \right\}\)                                              

\(\left( {a + b} \right)\in \left\{ {0;9;18} \right\}\)

\(\left( {a + b} \right) \in \left\{ {1;2;3} \right\}\)                                                 

\(\left( {a + b} \right)\in \left\{ {4;5;6} \right\}\)

A. \(b = 1\,;\,\,4\,;\,\,7\)

B. \(b = 2\,;\,\,5\,;\,\,8\)

C. \(b = 3\,;\,\,6\,;\,\,\,9\)

D. \(b = 0\,;\,\,3\,;\,\,6\,;\,\,9\)

\(3\)

\(4\)      

\(5\)                                    

\(6\)

\(x = 0;y = 6\)  

\(x = 6;y = 0\)      

\(x = 8;y = 0\)         

\(x = 0;y = 8\)