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

### Instruction:
 Mary alitumia galoni 15 za mafuta wiki hii. Wiki iliyopita alitumia 20% chini. Alitumia mafuta kiasi gani jumla kwa wiki mbili?


### Response:
 Ikiwa Mary alitumia 20% chini ya mafuta wiki iliyopita kuliko alivyotumia wiki hii, basi alitumia galoni 15 * 0.2 = <<15*0.2=3>>3 za mafuta wiki iliyopita.
Hii inamaanisha kwamba alitumia galoni 15 - 3 = <<15-3=12>>12 za mafuta wiki iliyopita.
Jumla, Mary alitumia galoni 15 + 12 = <<15+12=27>>27 za mafuta kwa wiki mbili.