Correct. Subtract 9 from all parts: $\displaystyle{1}-{9}\le{4}{d}+{9}-{9}<{21}-{9}\usepackage{cmbright}\Huge\$

Simplify to $\displaystyle-{8}\le{4}{d}<{12}\usepackage{cmbright}\Huge\$ , then divide all parts by 4.

The result is $\displaystyle-{2}\le{d}<{3}\usepackage{cmbright}\Huge\$ . The graph contains all the points between $\displaystyle-{2}\usepackage{cmbright}\Huge\$ and 3.

This includes the endpoint $\displaystyle-{2}\usepackage{cmbright}\Huge\$ , and does not include 3.