2011 Fermat Problem 21

The positive integers are arranged in increasing order in a triangle, as shown. Each row contains one more number than the previous row. The sum of the numbers in the row that contains the number 400 is

\begin{array}{c} 1 \\ 2 \quad 3 \\ 4 \quad 5 \quad 6 \\ 7 \quad 8 \quad 9 \quad 10 \\ 11 \quad 12 \quad \cdots \end{array}

\textbf{(A)}\ 10\,990\quad \textbf{(B)}\ 12\,209\quad \textbf{(C)}\ 9855\quad \textbf{(D)}\ 10\,976\quad \textbf{(E)}\ 11\,368

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Fermat contests here.