2004 AMC 8 Problem 11

The numbers -2, 4, 6, 9 and 12 are rearranged according to these rules:

\text {The largest isn't first, but it is in one of the first three places.} \text {The smallest isn't last, but it is in one of the last three places.} \text {The median isn't first or last.}

What is the average of the first and last numbers?

\textbf{(A)}\ 3.5 \qquad \textbf{(B)}\ 5 \qquad \textbf{(C)}\ 6.5 \qquad \textbf{(D)}\ 7.5 \qquad \textbf{(E)}\ 8

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.