A hummingbird hovers by exerting a downward force on the air equal, on average, to its weight. By Newton's third law, the air exerts an upward force of the same magnitude on the bird's wings. Find the average mechanical power (in W) delivered by a 4.40 g hummingbird while hovering if its wings beat 70.0 times per second through a stroke 3.98 cm long.