Directions: The following questions are accompanied by two statements (I) and (II). You have to determine which statements(s) is/are sufficient/necessary to answer the following question.

What is the speed of the boat in still water?

I. The boat covers 20 km in 5 hrs in downstream.

II. The boat covers 20 km distance in 10 hrs in Upstream.

III. The speed of the stream is one - third of that of the boat in still water.