 
<translate> Tunanin: Tsarin tafkin shine 4 * 15 = 60 mil. Yana yin iyo a gudun 60 / 20 = 3 mph. Don haka yana yin tuƙi da saurin 3 * 2 = 6 mph. Wannan yana nufin yana daukan shi 60 / 6 = 10 hours zuwa raft a kusa da tafkin. <eng> Reasoning: The perimeter of the lake is 4 * 15 = 60 miles. He swims at a speed of 60 / 20 = 3 mph. So he rows at a speed of 3 * 2 = 6 mph. That means it takes him 60 / 6 = 10 hours to row around the lake. 