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

### Instruction:
A store sells pencils and erasers. It has a rule that for every pencil you buy, you must buy 2 erasers which cost 1/2 the price of the pencils. If they sold 20 pencils and earned $80, how much do erasers cost?

### Response:
 Waliuza mafuta ya kufutia 40 kwa sababu 20 x 2 = <<20*2=40>>40
Hivyo, waliingiza $40 kutokana na kuuza mafuta ya kufutia kwa sababu 40 x 1 = <<40*1=40>>40
Hivyo, mafuta ya kufutia yanagharimu $20 kwa sababu 80 - 40 = <<80-40=40>>40
Hivyo, mafuta ya kufutia 1 yanagharimu $1 kwa sababu 20 / 20 = <<20/20=1>>1