1 5/6 : (2/3 - 2/7) = 4 целых 13/16.
1) 2/3 - 2/7 = 14/21 - 6/21 = 8/21
2) 1 5/6 : 8/21 = 11/6 · 21/8 = (11·7)/(2·8) = 77/16 = 4 целых 13/16
12т-4ц=12т4ц
9кг+8т=17т