Two boats start together and race across a 72 km wide lake and back. Boat A goes acrossat 72 km/h and returnsat 72 km/h. Boat B goesacross at 36 km/h, and itscrew, realizing how far behind it is getting, returnsat 108 km/h. Turnaroundtimes are negligible, and the boat that completes the round-tripfirst wins. What is the average velocity of the winning boat?