a) \({3 \over 5} - {-7 \over {10}} - {{13} \over { - 20}}=\frac{12}{20}+\frac{14}{20}+\frac{13}{20}=\frac{39}{20}\)

b) \({3 \over 4} + {{ - 1} \over 3} - {5 \over {18}}=\frac{27}{36}-\frac{12}{36}-\frac{10}{36}=\frac{5}{36}\)

c) \({3 \over {14}} - {5 \over { - 8}} + {{ - 1} \over 2}=\frac{12}{56}+\frac{35}{56}-\frac{28}{56}=\frac{19}{56}\)

d) \({1 \over 2} + {1 \over { - 3}} + {1 \over 4} - {{ - 1} \over 6}=\frac{6}{12}-\frac{4}{12}+\frac{3}{12}+\frac{2}{12}=\frac{7}{12}\)