Sandy is younger than Molly by 20 years. If the ratio of their ages is 7:9, how old is Sandy?  Choose the most appropriate option.
A) 42
B) 49
C) 56
D) 63
E) 70

Rationale: "let sandy ' s age be 7 x and let molly ' s age be 9 x . 9 x - 7 x = 20 x = 10 sandy is 70 years old . the answer is e ."
Answer: E