A tree is 40 ft above the ground at its highest point and its roots extend 15 ft below the ground. What is the distance from the top of the tree to the deepest part of its roots?

What the question is really asking

You are finding one straight up-and-down distance that goes from a point above ground to a point below ground.

Represent the heights relative to ground level

Treat ground level as $0$.

• Top of the tree: $+40$ ft
• Deepest root: $-15$ ft

Compute the distance between the two points

Distance on a number line is the difference between the values: $$|40 - (-15)| = |55| = 55$$

So the top-to-root distance is $55$ ft.