"Juan can paint a 3600 - square foot house in 12 days, and Carissa can do the same job in 8 days. How long will it take them to paint a 3600 square foot house if they worked together?"
Juan paints 300 square feet per day. Carissa paints 450 square feet per day.
Together they paint 750 square feet per day.
3600/750 = 4.8 days or 4 days, 19 hours and 12 minutes.
(If I am correct, please thank me )