Add and simplify.

$\displaystyle\frac{{{3}{x}}}{{{5}{x}{{y}}^{{4}}}}+\frac{{{6}{{x}}^{{2}}}}{{{15}{{x}}^{{2}}{y}}}\usepackage{cmbright}\Huge\$

Domain all x, $\displaystyle{x}\ne{0}\usepackage{cmbright}\Huge\$ , all $\displaystyle{y}\usepackage{cmbright}\Huge\$ , $\displaystyle{y}\ne{0}\usepackage{cmbright}\Huge\$