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

### Instruction:
In a day, Sam hunts 6 animals. Rob hunts half as many animals as Sam. Mark hunts 1/3 of the total of what Rob and Sam hunt. If Peter hunts 3 times as many animals as Mark does, how many animals do they all hunt in a day?

### Response:
Rob hunts 1/2 * 6 animals/day = <<1/2*6=3>>3 animals/day.
Rob and Sam hunt 3 animals/day + 6 animals/day = <<3+6=9>>9 animals/day in total.
Mark hunts 1/3 * 9 animals/day = <<1/3*9=3>>3 animals in a day.
Peter hunts 3 * 3 animals/day = <<3*3=9>>9 animals in a day.
All of them hunt 3 animals/day + 6 animals/day + 3 animals/day + 9 animals/day = <<3+6+3+9=21>>21 animals in a day.
#### 21