a) You know the height of the arch is 9m, this gives b. You also have x intercepts of (10,0) and (-10,0), with this information you can solve for a in y=ax^2+b

b) C has the same x value as E so you can sub that value into the equation of the curve and find the coordinates for E. You should then be able to find the difference between the height of the man and the point on the arch

c) F and G have the same y value as H so you can sub that value into the equation of the curve like before. Once you have an x value you can find the required length