emergently easy xquerry and xpath with stylus

i need the xquery and xpath for the following: 1- titles of book ordered by " mark" ( customer) 2- sum ( total) price of books writen by " joe " ( author name) and sold on 24-07-2008 3- name of customers who ordered " sciences" ( categori name) books u can find an attached copy of the XML file where these should be done i need it as soon as possible im not looking for minimum bids, i will pay full price as soon as the project is done by not more than 1 day