To find the difference in elevation between the top of the apple tree and the tips of its roots, you can add the height of the tree above ground to the depth of its roots below ground.
The height of the apple tree is 3.6 feet above ground, and the roots extend 1.75 feet below ground.
Now, add these two measurements together:
\[ \text{Difference in elevation} = \text{Height of tree} + \text{Depth of roots} = 3.6 , \text{feet} + 1.75 , \text{feet} \]
Calculating that:
\[ 3.6 + 1.75 = 5.35 , \text{feet} \]
Therefore, the difference in elevation between the top of the apple tree and the tips of its roots is 5.35 feet.