1. The problem statement, all variables and given/known data A parabolic arch spans a stream 200 feet wide. How high must the arch be above the stream to give a minimum clearance of 40 feet over a channel in the center that is 120 feet wide? 2. Relevant equations 3. The attempt at a solution They are asking for the k value right? If I place the parabola starting from x=0,y=0 then the vertex is at (100,40+n). When x=40,y=40. x=160,y=40 I want to find out what y is when x=100. So I used the equation (x-h)^2 = a(y-k) (x-100)^2 = a(y-(40+n)) After using x=40 ,y=40 I get n=-3600/a And now I have no idea what to do .. Am I doing this right?