Combine like terms: $\displaystyle{4}{y}+{10}={42}\usepackage{cmbright}\Huge\$

Subtract 10 from both sides: $\displaystyle{4}{y}={32}\usepackage{cmbright}\Huge\$

Divide both sides by 4: $\displaystyle{y}={8}\usepackage{cmbright}\Huge\$