(1) If you order 8 copies at a time, the total cost of * * * is: 8×20×0.9+6= 150 yuan.

If 12 copies are ordered at one time, the total cost of * * is:12× 20× 0.8+12× 20× 0.8×10% = 211.

So the answer is:150; 2 1 1.2;

(2) Method 1: Let a * * * mail X books, divided into x 10 times.

18x+6？ x 10=930，

∴x=50

I ordered 50 books by mail.

Method 2: set up mail order y times,

( 18× 10+6)? y=930，

∴y=5，

So a * * * mail order book * * 5× 10 = 50 copies;

② The total cost of "mail order 10" is (18×10+6 )× 6 =186× 6 =1/6 yuan.

Total book price and postage for one-time mail order16× (1+10%) × 60 =17.6× 60 =1056 yuan.

From the economic point of view, we should choose one-time mail order.