Answer
$d(D, B) = 2$
Work Step by Step
$d(D, B)$ represents the distance between the points D and B on a number line.
If the coordinates of D and B are $d$ and $b$, respectively, then:
$d(D, B) = |d - b|$
Based on the given number line, the coordinates of D and B are $1$ and $-1$, respectively.
Use the formula above to obtain:
$d(D, B) = |1-(-1)| = |1+1| =|2|=2$
Thus,
$d(D, B) = 2$
