Question 1008001
sol can paint a house in 9 hours while ding can paint the same house in 16 hours. after 4 hours of working together, ding left and sol finish the job alone. How many hours did it take  sol to finish the job?
sol can pain a house in 9 hrs
ding can paint a house in 16 hrs 
sol 1 hrs painting =1/9 parts 
ding 1 hrs painting =1/16 parts
ding and sol 1 hrs together =1/9+1/16=25/144 parts
working together for 4 hrs =4x25/144=25/36 parts
reaming part=1-25/36=11/36 parts 
sol will finish work=11x9/36=11/4 days