Answer:
37 seconds to 20 feet, 40s to land
Explanation:
1. Substitute 20 as your y value. Values like height are typically y values.
2. 20=-20x+800
3. subtract both sides by 800
4. -740=-20x
5. Divide both sides by negative 20
6. x=37
7. repeat, but put 0 feet for landing
Hopefully you understand now!