AMC 8 2009 Problem 3

The graph shows the constant rate at which Suzanna rides her bike. If she rides a total of a half an hour at the same speed, how many miles would she have ridden?

$\textbf{(A)}\ 5 \textbf{(B)}\ 5.5 \textbf{(C)}\ 6 \textbf{(D)}\ 6.5 \textbf{(E)}\ 7$