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

### Instruction:
Bertha plays tennis. Every ten games, one of her tennis balls wears out. Every five games, she loses a ball. Every four games, she buys a canister of three balls. She started with two balls and gave one to her partner. After twenty games, how many tennis balls does she have?

### Response:
 Bertha anachakaa mipira 20 / 10 = <<20/10=2>>2 ya tennis katika michezo ishirini.
Anapoteza mipira 20 / 5 = <<20/5=4>>4 ya tennis katika michezo ishirini.
Ananunua chombo cha mipira 3 * 20 / 4 = <<3*20/4=15>>15 ya tennis katika michezo ishirini.
Bertha alianza na mipira 2 na akampa 1 mwenzi wake, hivyo ana mipira 2 + 15 - 2 - 4 - 1 = <<2+15-2-4-1=10>>10 ya tennis baada ya michezo ishirini.