A hot-air balloon ride has been set up so that a paying customer is carried straight up at 50 feet per minute for ten minutes and then immediately brought back to the ground at the
same rate. The whole ride lasts twenty minutes. Let h be the height of the balloon (in feet)
and t be the number of minutes since the ride began. Draw a graph of h versus t. What are
the coordinates of the vertex? Find an equation that expresses h in terms of t.