A toy is launched upward with a spring.its launch speed is 114m/s(upward),and it is under no power once launched.while flying upward,air resistance and gravity combine for an acceleretion of 11.4m/s/s(downwards). While falling back down ,air resistance and gravity combine for an acceleration of 8.8 m/s/s(downward). How long does it take to return to the ground?