Two boats start together and race across a 60-km-wide lake and back. boat a goes across at 60 km/h and returns at 60 km/h. boat b goes across at 30 km/h, and its crew, realizing how far behind it is getting, returns at 90 km/h. turnaround times are negligible, and the boat that completes the round trip first wins. (a) which boat wins and by how much? (or is it a tie? ) (b) what is the average velocity of the winning boat?