Answer:
1. 9 feet
2. The ground
3. Absolute values of opposite numbers are the same
Explanation:
Given
Distance up the apple tree = 9 feet up
Solving (a): How far he'll climb to come down
In this case, the distance from the ground up to the tree is the same distance back to the ground.
In other words;
Since he climbs 9 feet up, then he'll climb 9 feet down to the ground
Solving (b): What 0 represents
In this case, 0 represents the ground
Solving (c): Absolute values
The absolute values of opposite numbers (from negative to positive) are the same
Take for instance:


And so on...