Solution: Let the area of the original sector be x square centimeters.

( 1/2×n)÷360×π×(3r)？ =x+70

1/2×9×n÷360×π×r？ =x+70

9/2×x=x+70

7/2×x=70

x=20

A: The original area was 20 square centimeters.

8.

Solution: 80× 0.85× 8× 2 = 1088 m2.

π×(80+0.85×8)? -π×80? ≈356 1.5 1 m2

1088+356 1.5 1 = 4649.438+0 m2

A: It also needs a land area of 4,649.438+0 square meters.

nine

3.14× 0.75×100 = 235.5m.

14 13 ÷ 235.5 = 6 minutes

A: It will take six minutes.

10

3. 14×9? -3. 14×9? × 60/360 ≈ 2 12 m2

A: The area is 2 12 square meters.

1 1

3. 14×4? ×90/360-(4? -3. 14×4? × 90/360) = 9. 12 square unit

A: The area difference is 9. 12 square.