You can answer your question yourself with a little thought: Yes, setting up a coordinate system so that the center of the bridge is at the origin, the parabola is of the form y= ax^2. When x= 10, at the shore, y= -10 so you must have -10= a(10^2)= -100a. Dividing both sides by -100, a= -1/10 so the equation is y= -x^2/10. Now, in that coordinate system, "2 feet from the shore" is x= 8 or x= -8.