To divide a polynomial by a monomial, divide each term separately by the denominator.

$\displaystyle\frac{{{25}{{x}}^{{5}}{{y}}^{{4}}-{10}{{x}}^{{4}}{{y}}^{{3}}}}{{{5}{{x}}^{{4}}{{y}}^{{2}}}}=\frac{{{25}{{x}}^{{5}}{{y}}^{{4}}}}{{{5}{{x}}^{{4}}{{y}}^{{2}}}}-\frac{{{10}{{x}}^{{4}}{{y}}^{{3}}}}{{{5}{{x}}^{{4}}{{y}}^{{2}}}}={5}{x}{{y}}^{{2}}-{2}{y}\usepackage{cmbright}\Huge\$