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

### Instruction:
 一份18个月的杂志订阅正常价格为34美元。该杂志目前正在进行促销活动，订阅18个月的杂志每期可以享受0.25美元的优惠。促销订阅比正常订阅便宜多少美元？


### Response:
 每月发行两期杂志，所以总共有2 * 18 = <<2*18=36>>36期。
因此，促销订阅比正常订阅便宜36 * 0.25 = $<<36*0.25=9>>9美元。