he mass of the moon is 1/81 of the mass of the earth. Compared to the gravitational force that the earth exerts on the moon, the gravitational force that the moon exerts on the earth is

It is the same in magnitude and opposite in direction.

Explanation:

According Newton's Universal Law of Gravitation, the force that any mass exerts on any other one, is proportional to the product of their masses, inversely proportional tho the square of the distance between their centers, and acts along the line that joins both points.At the same time, this force is part of a action-reaction pair, according to Newton's 3rd Law, that states that for a force that one body exerts upon another, there exists an equal and opposite force exerted by the other body on the former one.So, we conclude that the gravitational force that the earth exerts on the moon is equal in magnitude and opposite in direction to the one that the moon exerts on the earth.

The car would move to the right with 150 n of force. the 150 n of force from friction and air resistance slows the car from moving to the right with 300 n of force.

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current