Where can I catch the Lanzhou airport bus?

There are four bus lines at Zhongchuan Airport:

1 line originated from No.588, Donggang West Road, Chengguan District, Civil Aviation Ticket Office; 05: 15-20:30, buses run every 30 minutes;

Line 2 runs every hour at Xijin West Road 196 Kunyi Boutique Hotel (opposite Lanzhou West Station), 09:30-2 1:30;

Line 3 is at Qingshuiqiao Home Inn; 06:00、 10:00、 15:00、 17:00

Where is Line 4? Linxia State Supply and Marketing Cooperative No.82, Hongyuan Road, Linxia City (No.2 bus only, 06:00 and 08:00)