You may have added the numerators and multiplied the denominators. To add these fractions, rewrite each with the least common denominator, which is $\displaystyle{7}{x}\cdot{2}{y}={14}{x}{y}\usepackage{cmbright}\Huge\$ . Start with:

$\displaystyle\frac{{6}}{{{7}{x}}}+\frac{{3}}{{{2}{y}}}=\frac{{6}}{{{7}{x}}}\cdot\frac{{{2}{y}}}{{{2}{y}}}+\frac{{3}}{{{2}{y}}}\cdot\frac{{{7}{x}}}{{{7}{x}}}\usepackage{cmbright}\Huge\$

Simplify the numerators and add them.