Suppose we have a river of width 100 feet and two swimmers who both swim at the same speed of 5 feet per second through the water. The river's current flows along its length at a steady rate of 3 feet per second.
The first swimmer stays on one side of the river, swimming upstream a distance (measured along the bank) exactly equal to the width of the river (i.e., 100 feet), then swimming back to the same starting point. How much time does this swimmer take to complete the round trip?