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

### Instruction:
 蒂娜有12支粉色的钢笔。她比粉色钢笔少9支绿色钢笔。蒂娜比绿色钢笔多3支蓝色钢笔。蒂娜总共有多少支钢笔？


### Response:
 通过从12中减去9来找到绿色钢笔的数量：12 - 9 = <<12-9=3>>3支。
通过将绿色钢笔的数量加上3来找到蓝色钢笔的数量：3 + 3 = <<3+3=6>>6支。
现在将每种颜色的钢笔数量相加来找到总共的钢笔数量：3 + 6 + 12 = <<3+6+12=21>>21支。