Appendix A - Review - A.1 Algebra Essentials - A.1 Assess Your Understanding - Page A11: 46

$d(C,A)=3$.

The coordinate of point $C$ is $=0$ The coordinate of point $A$ is $=-3$ The distance between $C$ and $A$ is $d(C,A)=\left | -3-0 \right |$ Simplify. $d(C,A)=\left | -3 \right |$ $d(C,A)=3$ Hence, the distance between $C$ and $A$ is $3$.