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

### Instruction:
Jack is ordering custom baseball caps for him and his two best friends. Jack's head is 12 inches in circumference. Charlie's head is 9 inches more than half the circumference of Jack's head. Bill's head is 2/3 the circumference of Charlie's head. How many inches in circumference is Bill's head?

### Response:
 Kwanza tafuta nusu ya kipenyo cha kichwa cha Jack: inchi 12 / 2 = <<12/2=6>>6.
Kisha tafuta ukubwa wa kichwa cha Charlie: inchi 6 + 9 = <<6+9=15>>15.
Kisha tafuta ukubwa wa kichwa cha Bill: inchi 15 * (2/3) = <<15*(2/3)=10>>10.