CGPSC Prelims Paper II 2020 Solved Paper

The following question consists of three statements. You have to study the question and the statements, and decide which of the statements is/are necessary to answer the question.
What is the speed of the current?
I. Speed of the boat is 8 km/hr in still water
II. The boat runs at a speed of 11 km/hr downstream
III. The difference between the speeds of the boat while travelling in still water and down-stream is 3 km/hr