Appendix A - Review - A.1 Algebra Essentials - A.1 Assess Your Understanding - Page A11: 48

$d(C,E)=3$

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