How long it would take to complete the work at the same rate?

A work crew of 3 people requires 3 weeks and 2 days to do a certain job. How long would it take a work crew of 4 people to do the same job if each person of both crews works at the same rate as each of the others? Note : each week contains six work days.

MetroEye: This problem is  the work-person-rate problem.
i.e; W₁/(M₁×H₁) = W₂/(M₂×H₂)
where W is work to be done,  M is the number of persons required, Hour is time required. 

Here as the work done is same W₁ = W₂
=> M₁×H_{1 =} M₂×H₂
H₁= 3 weeks 2 days = 3×6+2=20 days
=> 3×20= 4 × H₂
H₂ = 60÷4 = 15 days = 2 weeks 3 days
So 4 people should work 2 weeks and 3 days to do the same job.