In the given frequency table, what is the class size of each class?

A) 12

B) 13

C) 11

D) 10

\begin{tabular}{|c|c|} \hline Income (in millions) & Frequency \\ \hline 918 & 12 \\ \hline 1928 & 9 \\ \hline 2938 & 7 \\ \hline 3948 & 8 \\ \hline 4958 & 7 \\ \hline 5968 & 7 \\ \hline \end{tabular}