(b) Figure 1 shows part of the graph of the quadratic function y = -x2+ 7x + 18. ( -2,0 ) (9,0) Figure 1 (i) Explain why the graph of the quadratic function y = -x2 + 7x + 18 is n-shaped. [1] (ii) Write down the y-intercept. [1] (iii) Find the equation of the axis of symmetry of the parabola given by y= -x4+ 7x+ 18, explaining your method. [2] (iv) Use your answer to part (b) (iii) to find the coordinates of the vertex of the parabola given by y = -x2 + 7x + 18. [2] This