-0,21x-15_56=3_16+257_800x

а почему 12_17

-0,21x - 15/56 = 3/16 + 257/800x-21/100x - 257/800x = 3/16 + 15/56-21/100x - 257/800x= - (21/100 + 257/800)x= - (168/800 + 257/800)x=- 425/800x =    = - 17/32x3/16 + 15/56 = 21/112 + 30/112 = 42/112 =  6/16 = 3/8-17/32x = 3/8x = 3/8 : (-17/32) = -3/8*32/17 = -12/17