80:10.3:6.5:2.7:10.5=35

80 ∶ 10 = 8
8 × 3 = 24
24 ∶ 6 = 4
4 × 5 = 20
20 ∶ 2 = 10
10 × 7 = 70
70 ∶ 10 = 7
7 × 5 = 35

Ответ: 35