4. A stone dropped in a still pond creates a circular ripple whose radius increases at a constant rate of 2 ft/s. At what rate is the area enclosed by the ripple increasing 10s after the stone strikes the pond? a) 60x ft2/s b) 200# ft2 / s c) 120# ft2 /s d) 40x ft2 / s e) 80x ft2 /s 5. A balloon rises vertically at the rate of 8ft/s. A person on the ground 40 ft away from the spot below the rising balloon watches the balloon ascend; at what rate is the distance between balloon and observer changing when the balloon is 30 ft above ground? a) 4.8 ft/s b) 0.208 ft/s c) 5.0 ft/s d) 5.4 ft/s e) 4V2 ft/s 6. Find the point of inflection of f(x) = x3 + 6x2 - 5x + 10. a) (-2,36) b) (2, 32) c) (0, 10) d) (2,31) e) (-2, -17)