All of the members of our spray-painting team paint at the same speed. If 20 team members can paint a 4800 square foot wall in 36 minutes, then how many minutes would it take for 9 team members to paint a 4200 square foot wall?

It takes 70 minutes for 9 team members (painting 60 sq ft per minute) to paint a 4200 sq ft wall.

Step-by-step explanation:

4800 : 20 = 240 sq ft per team member in 36 minutes

240 : 36 = 6.67 sq ft per team member in 1 minute

6.67 * 9 = 60 sq ft per 9 team members in 1 minute

4200 : 60 = 70 minutes (or 1 hour and 10 minutes)