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?
First find half the circumference of Jack's head: 12 inches / 2 = <<12/2=6>>6 inches
Then find how big Charlie's head is: 6 inches + 9 inches = <<6+9=15>>15 inches
Then find how big Bill's head is: 15 inches * 2/3 = <<15*2/3=10>>10 inches
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