How should I write this XPath statement

How would I write an XPath statement,executed from the 'Order' level to access the following:

+ Order
  + item
    - price
    - quantity
    - type

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I wrote the following, but since I am executing this from the
Orders level, it seems to get confused on the Cardinality.  
How should I write this ?

fn:sum($Orders/item[type = 'Shoe']/quantity*price)

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Thanks