If L, M, and S represent the large, medium, and small circumferences, then their total is $\displaystyle{L}+{M}+{S}={186}\usepackage{cmbright}\Huge\$ . The large pan is twice the small: $\displaystyle{L}={2}{S}\usepackage{cmbright}\Huge\$ , or $\displaystyle{L}-{2}{S}={0}\usepackage{cmbright}\Huge\$ . The medium is 18 centimeters greater than the small: $\displaystyle{M}={S}+{18}\usepackage{cmbright}\Huge\$ , or $\displaystyle{M}-{S}={18}\usepackage{cmbright}\Huge\$ .