Multiply both sides by 5 to clear the fractions: $\displaystyle{y}+{55}={15}-{3}{y}\usepackage{cmbright}\Huge\$

Subtract 55 from both sides: $\displaystyle{y}=-{40}-{3}{y}\usepackage{cmbright}\Huge\$

Add $\displaystyle{3}{y}\usepackage{cmbright}\Huge\$ to both sides: $\displaystyle{4}{y}=-{40}\usepackage{cmbright}\Huge\$

Divide both sides by 4: $\displaystyle{y}=-{10}\usepackage{cmbright}\Huge\$