Hi Mike.

Let H = the weight of the head and let B = the weight of the body.

"The tail of a fish weighs 9 oz. The head weighs as much as the tail and half of the body."

H = 9 + (1/2)B

"The body weighs as much as the head and tail combined."

B = H + 9

"What is the total weight of the fish?"

Find B + H + 9.

To solve this, we first eliminate one of the variables (I'll choose B) by substituting it out:

H = 9 + (1/2) (H + 9)

Solve for H. When you have that, you can solve for B and then add B + H + 9 to get the final answer.

Hope this helps,
Stephen La Rocque.