In Exercises 15-19, write a quadratic function in standard form whose graph satisfies the given conditions. 15. vertex: (-5, 4) 16. x-intercepts: 2 and 7 17. passes through (-3, 0), (1, 0), and (-1, 8) 18. axis of symmetry: x = -3 19. passes through: (-4, 0) and (4, 0)