question below. Part a: Circle the quadratic function that has a graph that opens downward. f(x) = x-3x-4 f(x) = x+4x+10 Part b: Circle the quadratic function that has a y-intercept at (0,9). f(x) = x+6x+9 f(x) = x+9x+18 Part c: Circle the coordinate pair that represents the vertex of function f. (-3,0) (-2,1) (-1,0)