(580 в-25)*90+490 =850 (580 в-25)*90=850-490 (580 в-25)*90=360 580в-25=360:90 580в-25=4 580в=4+25 580в=28=9 в=580:29в=20
(580 в-25)*90+490 =850
(580 в-25)*90=850-490
(580 в-25)*90=360
580в-25=360:90
580в-25=4
580в=4+25
580в=28=9
в=580:29
в=20