Mark Twain sat on the deck of a river steamboat. As the paddle wheel turned a point on the blade moved so that the distance, d, from the water's surface was a sinusoidal function of time. When Twain's stopwatch read 4 seconds, the point was at its highest, 16 feet above the water's surface. The wheel's diameter was 18 feet, and it completed a revolution every 10 seconds.
What was the first positive value of t, at which the point was on the water’s surface? Round to the nearest tenth of a second.