Answer:
He started climbing 9 feet up into the tree, so we can assume that the initial position is 9ft above the ground.
Then if he wants to get back into the ground, he must "descend" or climb down 9 ft again.
Then the integer is -9 (because he is climbing down now).
In this case, the 0 represents that he does not move.
So the integer 0 is related to: +0ft or -0ft
This means that he climbs up 0ft or down -0ft, which is the same as not moving at all.
