-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 = = - 17/32x
3/16 + 15/56 = 21/112 + 30/112 = 42/112 = 6/16 = 3/8
-17/32x = 3/8
x = 3/8 : (-17/32) = -3/8*32/17 = -12/17