Answer:
35 below the cave entrance.
Step-by-step explanation:
Let the cave entrance be the level from which the positions of Anna will be covered.
Anna is 40 feet below the cave entrance.
That means her position will be considered as (-40) feet.
Then she descends 13 feet then the position of Anna will be = -40 - 13 = -53 feet
Further she ascends 18 feet so her position will be = -53 + 18 = -35 feet
Therefore, the new position of Anna is 35 below the cave entrance.