Liu Ming wants to buy some school things. According to the list, if he buys twelve exercise books, four knives, five pens, double rulers and a pencil-box, he will pay . Thing Knife Pen Exercise book Ruler Pencil-box Price ¥2.50 ¥15.00 ¥3.00 ¥1.50 ¥16.00 Good news : If you spends more than one hundred yuan in buying pens, you will enjoy a 40% off for the whole list.