1991 AHSME Problem 16

One hundred students at Century High School participated in the AHSME last year, and their mean score was 100. The number of non-seniors taking the AHSME was 50\% more than the number of seniors, and the mean score of the seniors was 50\% higher than that of the non-seniors. What was the mean score of the seniors?

\textbf{(A) } 100\qquad \textbf{(B) } 112.5\qquad \textbf{(C) } 120\qquad \textbf{(D) } 125\qquad \textbf{(E) } 150

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