Marco and his sister are rummaging through a large box of books. Their younger brother also wants to see what’s inside the box. Marco pulls the box away from his brother, applying a force of 38 N to the left. His sister helps him by applying an additional force of 36 N to the left. Their brother applies a force of 35 N to pull the box in the opposite direction. The box weighs 22 kg. Determine the acceleration of the box.