pushing on something that pushes back = action and reaction.
Gravity is non contact. Action at a distance. Hence stones wil fall if dropped.
Answer:
B. 30m
Explanation:
This is because when a wave interferes constructively with another wave, they will add since constructive relates to joining or building up.
So, 10m + 20m equals a 30m wave.
The upper back muscles being worked while using a rowing machine .your upper trapezius and rhomboids located between your shoulder blades, and latissimus dorsi located beneath the armpits