$\frac{4}{20}$ + $\frac{16}{42}$ + $\frac{6}{15}$ + $\frac{-3}{5}$ + $\frac{2}{21}$ + $\frac{-10}{21}$ + $\frac{3}{20}$
= $\frac{7}{20}$ + $\frac{-1}{5}$ + $\frac{-8}{21}$ + $\frac{8}{21}$
= $\frac{7}{20}$ + $\frac{-1}{5}$
= $\frac{7}{20}$ + $\frac{-4}{20}$
= $\frac{3}{20}$