Consider the following quadratic function and its graph. f(x) = x2 – 4x – 21 On a coordinate plane, a parabola opens up. It goes through (negative 4, 8), has a vertex around (2, negative 21), and goes through (8, 8). What is the solution of the following quadratic inequality? x2 – 4x – 21 ≤ 0 A number line going from negative 8 to 8. Open circles are at negative 3 and 7. The line between the circles is shaded. A number line going from negative 8 to 8. Closed circles are at negative 3 and 7. The line between the circles is shaded. A number line going from negative 8 to 8. Open circles are at negative 3 and 7. The line to the left of negative 3 and to the right of 7 is shaded. A number line going from negative 8 to 8. Closed circles are at negative 3 and 7. The line to the left of negative 3 and to the right of 7 is shaded.