I feel the answer should be E.

As from all the facts given we cannot deduce partick and dodi's rate of doing work (work done per day)

If we had information like patrick did 20% of work and rest by dodi, we would have been able to find the answer.

Any comments..?

Yeah.. I also think we cannot reach av definite answer as the percentage of work finished by Patrick before leaving the job is not stated.

How about this...

Let k be the fraction of work Patrick finishes before he leaves the job.

Therefore, patrick does k (fraction) of the job in 4 days
So patrick will do the whole job in 4/k days.

From 1)

Dodi finishes 1-k job in 8 days, so Dodi will finish the whole job in 8/(1-k) days

From 1, nothing is clear.

From 2)
1/P+1/D= 3/20
we know P=4/k but we dont know D
so not sufficient.

Now if u combine 1 and 2,
P=4/k, D=8/(1-k)
so k/4+(1-k)/8=3/20
therefore, k=1/5
hence we know Patrick can finish the job in 20 days.

Hence the answer is C.