Tính 3/7 + 1/2 - (-3/70)

$$\begin{gathered} a)\frac{3}{7}+\frac{1}{2}-\frac{-3}{70} \\ b)\frac{5}{15}+\frac{4}{-12}+\frac{1}{7}-\frac{1}{-6} \end{gathered}$$