A year ago, the ratio of Betty's and Chi's age was 6:7 respectively. Four years hence, this ratio would become 7:8. How old is Betty?
Choose the correct option.
A) 34 years B) 29 yeras C) 25 years D) 30 years E) 40 years
(b-1)/(c-1)=6/7;   (b-1+4)/(c-1+4)=7/8;   by solving them we get   8b-7c=-3   7b-6c=1   then solving these eq we get   c7 -6= 
<gadget id="calculator">7 -6</gadget>
<output>1</output>
1   then solving these eq we get   c=29   b=25   ANSWER:25 years
<result>C</result>
A year ago, the ratio of Betty's and Chi's age was 6:7 respectively. Four years hence, this ratio would become 7:8. How old is Betty?