It takes 36 minutes for 7 people to paint 4 walls. How many minutes does it take for 9 people to paint 7 walls?

Question

I really don't get this problem, please help!

Answer 1

4 walls need 262 people/minutes (7)(36)

1 wall takes 63 people/minutes (262/4)

7 walls need 441 people/minutes (63)(7)

9 people could do that in 49 minutes (441/9)