Dawei wanted to buy a cell phone, and he asked Liu Yang how mush money he needed. Liu Yang told him the price of a cell phone ranged from several thousand to several hundred kuai depending on the quality. But Dawei had only 30 kuai depending on the quality. But Dawei had only 30kuai with him, with which he could barely buy a cell phone case. Dawei had to go to the bank and change some money. Since it’s Dawei’s first time going to a Chinese bank, what should Dawei say in the bank？