(0,7х - 4/7) * 1 2/3 = 6,45
0,7х - 4/7 = 6,45 : 5/3 = 645/100 : 5/3 = 645/100 * 3/5
0,7х - 4/7 = 129/100 * 3/1 = 387/100
0,7х = 387/100 + 4/7 = 2709/700 + 400/700
0,7х = 3109/700
х = 3109/700 : 7/10 = 3109/700 * 10/7
х = 3109/70 * 1/7 = 3109/490
х = 6,35