Solving 'Before & After' questions using algebra

1. A farmer had some chickens and ducks. The ratio of the number of chickens to the number of ducks was 5:7. After buying another 18 of each type of chickens and ducks, the ratio of the number of chickens to the number of ducks became 7:9.
   a) How many chickens did he have at first?
   b) What was the total number of chickens and ducks he had after that?
   
   
2. May had 3/4 as much money as Olivia at first. May received $24 and Olivia spent $15 from her mother. As a result, May had 7/9 as much money as Olivia. How much money did May have now?

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