\(\displaystyle{\rm{A}} = {6 \over 7} + {1 \over 7}.{2 \over 7} + {1 \over 7}.{5 \over 7} \)
\(\displaystyle= {1 \over 7}.\left( {6 + {2 \over 7} + {5 \over 7}} \right) \)
\(\displaystyle= {1 \over 7}.7 = 1\)
\(\displaystyle B = {4 \over 9}.{{13} \over 3} - {4 \over 3}.{{40} \over 9} \)
\(\displaystyle B = {4 \over 9}.{{13} \over 3} - {4 \over 9}.{{40} \over 3} \)
\(\displaystyle = {4 \over 9}.\left( {{{13} \over 3} - {{40} \over 3}} \right) \)
\(\displaystyle= {4 \over 9}.{{ - 27} \over 3} = {{4.( - 27)} \over {27}} = - 4\)
