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

### Instruction:
Brenda is a vet who needs to spay some cats and twice as many dogs. If she needs to spay 21 animals total today, how many cats does she need to spay?

### Response:
 Hebu c iwe idadi ya paka Brenda anahitaji kufanya upasuaji na d iwe idadi ya mbwa. Tunajua kwamba c + d = 21 na d = 2c.
Kwa kubadilisha equation ya pili katika equation ya kwanza, tunapata c + 2c = 21
Kwa kuunganisha vipengee kama, tunapata 3c = 21
Kwa kugawanya pande zote mbili na 3, tunapata c = 7