题目

People in the United States honor their parents with two special days: Mother’s Day, on the second Sunday in May, and Father’s Day, on the third Sunday in June.  Mother’s Day was announced a day for national celebration by President Woodrow Wilson in 1915. Ann Jarvis from Grafton, West Virginia, had started the idea to have a day to honor mothers. She was the one who chose the second Sunday in May and also began the custom of wearing a carnation(康乃馨). In 1909, Mrs. Dodd from Spokane, Washington, thought of the idea of a day to honor fathers. She wanted to honor her own fat应用题：阅读下列对话：张老师：“售货员，我买些梨．”售货员：“张老师，您上次买的那种梨都卖完了，我们还没来得及进货，但我建议您先买一些我们新进的苹果．”张老师：“好，和上次一样，也买30元钱的．”结账后，对照前后两次的电脑小票，张老师发现：每千克苹果的价格是梨的价格的倍，苹果的重量比梨少千克．试根据上面的对话和张老师的发现，分别求出梨和苹果的单价．