Answer:
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)