To find the net force acting on the runner, you need to consider the forces acting in opposite directions.
The runner exerts a force of 325 N to the right, and the air resistance exerts a force of 45 N to the left.
The net force can be calculated using the following equation:
Net Force = (Force to the right) - (Force to the left)
Net Force = 325 N - 45 N
Net Force = 280 N to the right
Therefore, the correct response is:
280 N