find the distance between a and b on the number line below.

Explanation:

Step1: Identify the coordinates

The coordinate of point A is -9 and the coordinate of point B is -1.

Step2: Use the distance formula on number - line

The distance $d$ between two points $x_1$ and $x_2$ on a number - line is $d=\vert x_2 - x_1\vert$. Here, let $x_1=-9$ and $x_2 = - 1$. Then $d=\vert-1-(-9)\vert$.

Step3: Simplify the expression

First, simplify $-1-(-9)=-1 + 9=8$. Then $\vert-1-(-9)\vert=\vert8\vert = 8$.

Answer:

8