Answer
(a) $-\frac{1}{30}$
(b) $\frac{43}{30}$
Work Step by Step
We find common denominators and reduce:
(a) $\displaystyle \frac{7}{10}-\frac{11}{15}=\frac{21}{30}-\frac{22}{30}=-\frac{1}{30}$
(b) $\displaystyle \frac{7}{10}+\frac{11}{15}=\frac{21}{30}+\frac{22}{30}=\frac{43}{30}$