Alizard is at the bottom of a 12 -foot well. each day it crawls up 5 feet, but each night it slips back 4 feet . after how many days will the lizard reach the top of the well?

12 feet

D1: 5 - 4 = 1 foot

D2: 1 + 5 = 6
       6 - 4 = 2 ft

D3: 2 + 5 = 7
       7 - 4 = 3 ft

D4: 3 + 5 = 8
       8 - 4 = 4 ft

D5: 4 + 5 = 9
       9 - 4 = 5 ft

D6: 5 + 5 = 10
       10 - 4 = 6 ft

Each day the lizard moves up 1 foot. If you double the day it moved up 6 feet then you will get the day it moved up 12 feet.
D6 × 2 = D12

It will take the lizard 12 days to reach the top of the well.