Final answer:
The force exerted by the sledgehammer is 750N, based on Newton's third law of motion, which indicates that every action has an equal and opposite reaction.
Step-by-step explanation:
The force exerted by the sledgehammer is 750N. According to Newton's third law of motion, every action has an equal and opposite reaction. When the construction worker hits the concrete with the sledgehammer, the sledgehammer applies a force to the concrete, and the concrete applies an equal and opposite force to the sledgehammer. Since the question states that the sledgehammer delivers a force of 750N, this is both the force exerted on the concrete and the reaction force on the sledgehammer itself, meaning the correct answer is option 1) 750N.