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

Subtract 15 from both sides: $\displaystyle{3}{y}={40}+{y}\usepackage{cmbright}\Huge\$

Subtract y from both sides: $\displaystyle{2}{y}={40}\usepackage{cmbright}\Huge\$

Divide both sides by 2: $\displaystyle{y}={20}\usepackage{cmbright}\Huge\$