Weighing a fish from its head, body and tail

A fish is cut into three parts. Its tail weighs $9$ ounces. Its head weighs as much as the tail plus half of the body. Its body weighs as much as the head and tail combined. What does the whole fish weigh, in ounces?

$72$ ounces. With $h=9+\tfrac b2$ and $b=h+9$, substitution gives $b=18+\tfrac b2$, so $b=36$, $h=27$, and $9+27+36=72$.