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

### Instruction:
 约翰每个月在一个庇护所做义工，每次3小时。他一年做多少小时的义工？


### Response:
 他一年做义工2*12=<<2*12=24>>24次。
所以他一年做义工24*3=<<24*3=72>>72小时。