At 9 a.m., Ryan had finished cutting \frac{1}{2} of his lawn. At 10 a.m., he had finished cutting \frac{7}{8} of his lawn. If Ryan cut his lawn at a constant rate, at what time did he finish?
Answer Choices
A. 10:15 a.m.
B. 11:20 a.m.
C. 10:20 a.m.
D. 10:30 a.m.
E. 11:40 a.m.