How can gravity be described as a scientific theory and a scientific law at the same time?

Can somebody explain to me how newton's 3rd law relates to momentum? ~ap physics 1

In the sport of parasailing, a person is attached to a rope being pulled by a boat while hanging from a parachute-like sail. a rider is towed at a constant speed by a rope that is at an angle of 15 ∘ from horizontal. the tension in the rope is 1900 n. the force of the sail on the rider is 30∘ from horizontal. what is the weight of the rider? express your answer with the appropriate units.

Gunpowder residue is most likely to show up where on a shooters hands