Below is an instruction that describes a task. Write a response that appropriately completes the request in Chinese. Please answer in Chinese.

### Instruction:
 弗兰克想为卧室买一盏新灯。最便宜的灯的价格是20美元，店里最贵的灯是最便宜的3倍。如果他目前有90美元，并购买最贵的灯，他会剩下多少钱？


### Response:
 最贵的灯的价格是20 * 3 = 60美元。
所以如果弗兰克买了那盏灯，他会剩下90 - 60 = 30美元。