AMC 8 2012 Problem 14

In the BIG N, a middle school football conference, each team plays every other team exactly once. If a total of 21 conference games were played during the 2012 season, how many teams were members of the BIG N conference? $\textbf{(A)}\hspace{.05in}6 \textbf{(B)}\hspace{.05in}7 \textbf{(C)}\hspace{.05in}8 \textbf{(D)}\hspace{.05in}9 \textbf{(E)}\hspace{.05in}10$