How can my friend go from the West Railway Station to Beijing International Airport?

Yes, both subway and shuttle bus are availble.

By shuttle bus: airport shuttle bus line 7 directly leads to the airport from the West Station.
By train: take subway line 7 to Shuangjing Station, where transfer to line 10 and get off at Sanyuanqiao. There it is easy to change to Airport Express Train to PEK.

If my friend takes the Line 7 Airport Shuttle Bus to Capital International Airport, how long would it take in the evening (dinner time) and what might the cost be? Where do you find the bus outside the West Train Station? I imagine there is a ticket window somewhere.

Actually, my friend never found the shuttle bus No. 7 from the West Train Station to the Airport. He took a taxi and it cost 300 Yuan.