2: 80÷4=20 (interval) 20-9= 19 19×2=38 (tree)

( 1) ( 18- 1) × 3 = 5 1 (2) ( 18+ 1) × 3 = 57 (3) 18 × 3 =

Four: 400 meters =40000 cm, 200 meters =20000 cm.

(40000 ÷ 40+1) × (20000 ÷ 40+1) = 501(watershed)

Little friend, you should think for yourself about any topic.