It will travel 21 miles upstream in three hours going down stream we can show 39 miles in the same amount of time find the speed of the current in the speed of the boat in Still water

Answer: The speed of the current is 3 miles per hour.The speed of the boat in still water is 10 miles per hourStep-by-step explanation:Let the speed of the boat be x miles per hourLet the speed of the current be y miles per hourSpeed = distance / timeIf the boat moves 39 miles downstream in 3 hours, then, the speed is39/3= 13 miles per hourLet us assume that it moved it moved in the same direction with the current hence, it moved in still waterThe total speed would be x + y. Thereforex + y = 13 - - - - - - -1If the boat moves 21 miles upstream in 3 hours, the the speed is21/ 3 = 7 miles per hourIt is assumed that it moved in the opposite direction to the current.The total speed would be x - y. Thereforex - y = 7 - - - - - - -2Adding equation 1 and equation 2, it becomes2x = 20x = 20/2 = 10 miles per houry = 13 - xy = 13 - 10 = 3 miles per hour