[tex]\displaystyle\bf\\C=\{0;~1;~2;~3;~4;~5;~6;~7;~8;~9\} ~~~Multimea~cifrelor\\\\A=\{0;~3;~6;~9\} ~~~Multimea~de~cifre~multiplu~de~3\\\\B=\{1;~2;~4;~5;~7;~8\}~~~Nultimea~celorlalte~cifre\\\\\textbf{Submultimile lui C de patru elemente cu 2 cifre multiplu de 3}\\\textbf{sunt submultimile care contin 2 cifre din A si 2 cifre din B}\\\\Numarul~lor~este:\\\\n=C_4^2\times C_6^2\\\\n=\frac{4\times3}{1\times2}\times\frac{6\times5}{1\times2}\\\\n=6\times15\\\\\boxed{\bf~n=90~de~submultimi}[/tex]