Final answer:
The force exerted by the 4.0 kg block on the 3.0 kg block is 10 N in the opposite direction.
Step-by-step explanation:
The force exerted by the 4.0 kg block on the 3.0 kg block can be determined using Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. This means that the force exerted by the 4.0 kg block on the 3.0 kg block is equal in magnitude and opposite in direction to the force exerted by the 3.0 kg block on the 4.0 kg block.
Therefore, the force exerted by the 4.0 kg block on the 3.0 kg block is also 10 N, but in the opposite direction.