Since it takes 5 people to paint 5 walls 20 minutes, that means that it would take 1 person 20 minutes to paint 1 wall. That also means that 2 people would take 20 minutes to paint 2 walls. So, it would take 9 people 20 minutes to paint 9 walls.
Ounces are typically used to measure liquid, so I would discourage choosing the top two. And, hopefully you know by now that an orange does not weigh 8 pounds.
