Time taken by Anu, Tanu and Manu to complete a job is in the ratio 5 : 8 : 10 
This means that their efficiencies are in the ratio 15 : 18 : 110 
Or, their efficiencies are in the ratios 8 : 5 : 4 
This means, for instance, if Anu can wash 8 plates in an hour, Tanu and Manu can wash 5 & 4
plates respectively in one hour. 
So, let us remodel the entire question over this imaginary scenario of washing plates… 
All three of them finish the job in 4 days working 8 hours per day. 
Anu, Tanu and Manu can wash 8, 5 and 4 plates respectively in an hour. 
So the total number of plates = (8+5+4)×4×8=17×4×8 
Anu and Tanu work together for 6 days, working 6 hours 40 minutes per day. 
The total number of plates washed by them = (8+5)×6×623=13×40 
So the remaining plates to be washed =17×4×8−13×40 
=4(17×8−130) 
=4(80+56−130) 
=4×6 
So, the question is, in how many hours can Manu wash 4×6 plates? 
We know that Manu can wash 4 plates in one hour. 
Therefore, he requires 6 hours to wash 4×6 plates.