A4=a1+3d=26
a8=a1+7d=68
a1=26-3d
26-3d+7d=68
4d=42
d=10,5
a1=26-3*10,5=-5,5
a21=-5,5+20*10,5=204,5
1) -2 1/8 * (-1 29/51) = -17/8 * (-80/51) = 10/3
2) -1 23/42 * 3 1/3 = -65/42 * 10/3 = -325/63
3) -4 2/3 * 6 = -14/3 * 6 = -28
4) 10/3 + (-325/63) = 210/63 - 325/63 = -115/63
5) -115/63 -(-28) = -115/63 + 28 = -115/63 + 1764/63 = 1649/63 = 26 11/63
ответ: 26 11/26
6)14 целых 1\10 10)34 целых 14\29
45 десятков.
Просто раздели 450 на 10.