Problem 6

$$\begin{array}{lcl} 6.\:When\:x\:is\:divided\:by\:7,\:the\:remainder\:is\:3. \\ What \:is\:the\:remainder\:when\:3x\:is\:divided\:by\:7\:?\\ \\ (A)\:8\\ \\ (B)\:6\\ \\ (C)\:4\\ \\ (D)\:7\\ \\ (E)\:9\\ \end{array}$$