6、The table below shows the score distribution of 50 students in Ye's class:
\begin{array}{c|c|c|c|c|c|c|c|c} \hline Score & 0 & 1 & 2 & 3 & 4 & \mathbf{5} & 6 & Total \\ \hline \begin{array}{c} Number \\ of \\ Students \end{array} & 4 & 4 & $\mathbf{5}$ & $A$ & 15 & $B$ & $\mathbf{2}$ & 50 \\
\hline
\end{tabular}

The average score in this exam is 3 points.
(1) How many students should be filled in the $A$ and $B$ columns?
(2) This exam consists of 3 questions, with the scoring distribution as follows: 1 point for the first question, 2 points for the second question, and 3 points for the third question. How many students answered at least 2 questions correctly?