Question
Zoe had some mochi balls. She sold 70% of her mochi balls and gave half of the remainder to her brother. After that, she bought 15 mochi balls and had a total of 21 mochi balls in the end. How many mochi balls did Zoe have at first?
4 m

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Zoe had some mochi balls. She sold 70% of her mochi balls and gave half of the remainder to her brother. After that, she bought 15 mochi balls and had a total of 21 mochi balls in the end. How many mochi balls did Zoe have at first?