Read the following information carefully and decide which information is/are necessary to answer the question. Find the speed of current I. Ratio of upstream speed and downstream speed is 3 : 5. II. Ratio of speed of boat and speed of current is 4 : 1. III. Boat goes to a place 45 km far and come back taking a total time of 5 hours.

To find the speed of the current, we need either the ratio of boat speed to current speed (statement II) or information to calculate both speeds. Statement III alone gives distance and total time, but we need the relationship between boat and current speeds to solve. Statement I provides the ratio of upstream:downstream speed (3:5), which combined with III's time data, or combined with II's ratio, is sufficient. Therefore, III with either I or II can solve for current speed.