Prefix and Infix notation

Write in prefix and infix notation: 4 7 x - * z +

So if they want me to write it in both prefix and infix notation, I can assumed that it what they have presented me is already written in postfix notation.

If it is written in postfix notation, the last value, +, is the root node. The first value, 4, would be the very bottom left child node.

But then I am unsure where to go from that information based on the solutions they have come up with.

Solutions:

Prefix: + * 4 - 7 x z

Infix: (4*(7-x)) + z

What is the next step to creating the correct tree based on the postfix notation?