$\frac{2}{3.5}$+$\frac{1}{5.6}$+$\frac{6}{6.12}$
=$\frac{1}{3}$-$\frac{1}{5}$+$\frac{1}{5}$-$\frac{1}{6}$+$\frac{1}{6}$-$\frac{1}{12}$
=$\frac{1}{3}$+(-$\frac{1}{5}$+$\frac{1}{5}$)+(-$\frac{1}{6}$+$\frac{1}{6}$)-$\frac{1}{12}$
=$\frac{1}{3}$-$\frac{1}{12}$
=$\frac{4}{12}$-$\frac{1}{12}$
=$\frac{3}{12}$
=$\frac{1}{4}$.