Set up a coordinate system so the x-axis is along the bridge roadway, the y-axis is vertical, and the origin, (0, 0), is half way between the two towers. Since the two towers are 150 m apart, they are at x= 75 and x= -75. The cable attaches to the towers 22 m above the roadway (y= 0) so the cable passes through the points (75, 22) and (-75, 22). Since the parabola is symmetric, we must have y= ax^2+ b. Also, the minimum is at (0, 7). Put x= 74, y= 22, and x= 0, y= 7 into equation to solve for a and b. Then, of course, evaluate y at x= 75- 15= 60.