\(\displaystyle{\rm{a)}}{{ - 1} \over {39}} + {{ - 1} \over {52}} = {{ - 4} \over {156}} + {{ - 3} \over {156}} = {{ - 7} \over {156}}\)
\(\displaystyle b){{ - 6} \over 9} + {{ - 12} \over {16}} = {{ - 2} \over 3} + {{ - 3} \over 4} \)\(\,\displaystyle= {{ - 8} \over {12}} + {{ - 9} \over {12}} = {{ - 17} \over {12}}\)
\(\displaystyle c){{ - 2} \over 5} - {{ - 3} \over {11}} = {{ - 22} \over {55}} - {{ - 15} \over {55}} \)\(\,\displaystyle =\frac{{ - 22}}{{55}} + \frac{{15}}{{55}} = \frac{{ - 22 + 15}}{{55}}= {{ - 7} \over {55}}\)
\(\displaystyle {\rm{d)}}{{ - 34} \over {37}}.{{74} \over { - 85}} = {{ (- 17).2.37.2} \over {37.( - 17).5}} = {4 \over 5}\)
\(\displaystyle {\rm{e)}}{{ - 5} \over 9}:{{ - 7} \over {18}} = {{ - 5} \over 9}.{{ - 18} \over 7}\)\(\,\displaystyle =\frac{{\left( { - 5} \right).\left( { - 2} \right)}}{{1.7}} = {{10} \over 7}\)
