Simplify $\frac{{{x}^{2}}-{{y}^{2}}}{{{(x+y)}^{2}}}\div \frac{{{(x-y)}^{2}}}{(3x+3y)}$

Simplify $\frac{1\tfrac{7}{8}\times 2\tfrac{2}{5}}{6\tfrac{3}{4}\div \tfrac{3}{4}}$