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

### Instruction:
 梅尔比凯瑟琳小三岁。当凯瑟琳两打岁时，梅尔多大？


### Response:
 当凯瑟琳两打岁时，她将会是2*12=<<2*12=24>>24岁。
如果梅尔比凯瑟琳小三岁，那么当凯瑟琳24岁时，梅尔将会是24-3=<<21=21>>21岁。