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

### Instruction:
 玛丽本周用了15加仑的燃料。上周她用了比这少20%。两周内她总共用了多少燃料？


### Response:
 上周，她用的燃料比本周少了15加仑 * 0.2 = <<15*0.2=3>>3加仑。
这意味着她上周用了15加仑 - 3加仑 = <<15-3=12>>12加仑的燃料。
玛丽两周内总共用了15加仑 + 12加仑 = <<15+12=27>>27加仑的燃料。