Final answer:
The normal force exerted by the platform on Stephanie is 726.2 N.
Step-by-step explanation:
The normal force exerted by the platform on Stephanie can be calculated using the formula:
Normal force (N) = Weight of Stephanie (W) + Weight of box
Weight of Stephanie = mass of Stephanie × acceleration due to gravity = 61 kg × 9.8 m/s² = 598.8 N
Weight of box = mass of box × acceleration due to gravity = 13 kg × 9.8 m/s² = 127.4 N
Therefore, the normal force exerted by the platform on Stephanie is 598.8 N + 127.4 N = 726.2 N.