\(\eqalign{
& a)\,\,\left( {{{ - 2} \over 3} + {3 \over 7}} \right):{4 \over 5} + \left( {{{ - 1} \over 3} + {4 \over 7}} \right):{4 \over 5} \cr
& = \left( {{{ - 2} \over 3} + {3 \over 7} + {{ - 1} \over 3} + {4 \over 7}} \right):{4 \over 5} \cr
& = \left[ {\left( {{{ - 2} \over 3} + {{ - 1} \over 3}} \right) + \left( {{3 \over 7} + {4 \over 7}} \right)} \right]:{4 \over 5} \cr
& = \left( {{{ - 3} \over 3} + {7 \over 7}} \right):{4 \over 5} \cr
& = ( - 1 + 1):{4 \over 5} = 0:{4 \over 5} = 0 \cr
& b)\,\,{5 \over 9}:\left( {{1 \over {11}} - {5 \over {22}}} \right) + {5 \over 9}:\left( {{1 \over {15}} - {2 \over 3}} \right) \cr
& = {5 \over 9}:{{2 - 5} \over {22}} + {5 \over 9}:{{1 - 10} \over {15}} \cr
& = {5 \over 9}:{{ - 3} \over {22}} + {5 \over 9}:{{ - 9} \over {15}} \cr
& = {5 \over 9}.{{22} \over { - 3}} + {5 \over 9}.{{15} \over { - 9}} \cr
& = {5 \over 9}.\left( {{{22} \over { - 3}} + {{15} \over { - 9}}} \right) \cr
& = {5 \over 9}.\left( {{{ - 22} \over 3} + {{ - 5} \over 3}} \right) \cr
& = {5 \over 9}.{{ - 27} \over 3} = {5 \over 9}.( - 9) \cr
& = {{5.( - 9)} \over 9} = - 5 \cr} \)
