KöMaL 2024 C1823

Smart Pali once went to the market to sell $30$ apples. He planned to ask for one kreuzer for every three apples, i.e. he expected a total income of $10$ kreuzers. At the market, he met another person who was also selling apples. The other seller also had 30 apples for sale, but he gave two apples for one kreuzer, so he was expecting a total income of $15$ kreuzers. Smart Pali got tired of the hustle and bustle of the market and handed over his $30$ apples to the other person, instructing him to sell them so that five apples would cost two kreuzers. Pali said he would come back later for his share of the income. $a)$ If this person sold all 60 apples following Pali's instructions and kept the income he originally expected, how many kreuzers were left for Smart Pali? $b)$ For how many kreuzers should the 60 apples have been sold in order for both sellers to receive their originally planned income?