(1)
:300 20 1/2 1 2 2 1 ( 2 ) 1 30 2 2 +2 : , , ,,, , . ( ) . . 15 . . ( ) ,~1 , ,~30/40. 30 + +2 . , (1 ) . 12 - ( 28 ), - . 20-30. 30,180" 2 2 . !